--- a/taskcluster/ci/artifact-build/kind.yml
+++ b/taskcluster/ci/artifact-build/kind.yml
@@ -5,17 +5,16 @@
 loader: taskgraph.loader.transform:loader
 
 kind-dependencies:
     - toolchain
 
 transforms:
     - taskgraph.transforms.build_attrs:transforms
     - taskgraph.transforms.build_lints:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 jobs:
     linux64-artifact/opt:
         description: "Linux64 Opt Artifact Build"
         index:
             product: firefox
@@ -41,10 +40,11 @@ jobs:
                 - builds/releng_base_linux_64_builds.py
             script: "mozharness/scripts/fx_desktop_build.py"
             secrets: true
             tooltool-downloads: public
             need-xvfb: true
             keep-artifacts: false
         dependencies:
             linux64-opt: build-linux64/opt
-        toolchains:
-            - linux64-node
+        fetches:
+            toolchain:
+                - linux64-node

--- a/taskcluster/ci/build-fat-aar/kind.yml
+++ b/taskcluster/ci/build-fat-aar/kind.yml
@@ -8,26 +8,24 @@ kind-dependencies:
     - build
     - toolchain
 
 transforms:
     - taskgraph.transforms.build:transforms
     - taskgraph.transforms.build_attrs:transforms
     - taskgraph.transforms.build_lints:transforms
     - taskgraph.transforms.build_fat_aar:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 job-defaults:
     attributes:
         artifact_map: taskcluster/taskgraph/manifests/fennec_geckoview.yml
     index:
         product: mobile
-    fetches: {}   # See build_fat_aar transform
     worker-type: b-linux
     worker:
         docker-image: {in-tree: android-build}
         max-run-time: 7200
         env:
             # Online in order to download the per-architecture AARs.
             GRADLE_USER_HOME: "/builds/worker/workspace/build/src/mobile/android/gradle/dotgradle-online"
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
@@ -53,26 +51,27 @@ job-defaults:
                 nightly-oak: nightly-oak
                 beta:
                     by-shipping-product:
                         devedition: aurora
                         default: beta
                 release.*: release
                 esr.*: esr
                 default: null
-    toolchains:
-        - android-gradle-dependencies
-        - android-ndk-linux
-        - android-sdk-linux
-        - linux64-clang
-        - linux64-rust-android
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - android-gradle-dependencies
+            - android-ndk-linux
+            - android-sdk-linux
+            - linux64-clang
+            - linux64-rust-android
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 jobs:
     android-geckoview-fat-aar/opt:
         description: "Android GeckoView multi-architecture fat AAR Opt"
         index:
             job-name: android-geckoview-fat-aar-opt
         treeherder:
             platform: android-4-0-geckoview-fat-aar/opt
@@ -85,18 +84,19 @@ jobs:
         worker:
             env:
                 PERFHERDER_EXTRA_OPTIONS: android-geckoview-fat-aar-opt
                 USE_ARTIFACT: '1'
                 MOZ_ARTIFACT_TASK: {task-reference: '<android-api-16-opt>'}
         run:
             actions: [get-secrets, build]
             config: ["builds/releng_base_android_64_builds.py"]
-        toolchains:
-            - linux64-sccache
+        fetches:
+            toolchain:
+                - linux64-sccache
 
     android-geckoview-fat-aar-nightly/opt:
         description: "Android GeckoView multi-architecture fat AAR Nightly"
         attributes:
             nightly: true
             enable-full-crashsymbols: true
             disable-push-apk: true
         shipping-phase: build

--- a/taskcluster/ci/build/android-stuff.yml
+++ b/taskcluster/ci/build/android-stuff.yml
@@ -35,17 +35,18 @@ android-geckoview-docs/opt:
         using: mozharness
         actions: [get-secrets, build]
         config:
             - builds/releng_base_android_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: android-geckoview-docs
         tooltool-downloads: internal
-    toolchains:
-        - android-gradle-dependencies
-        - android-sdk-linux
-        - linux64-node
+    fetches:
+        toolchain:
+            - android-gradle-dependencies
+            - android-sdk-linux
+            - linux64-node
     optimization:
         skip-unless-changed:
             - "mobile/android/**/*.java"
             - "mobile/android/gradle.configure"
             - "**/*.gradle"

--- a/taskcluster/ci/build/android.yml
+++ b/taskcluster/ci/build/android.yml
@@ -26,26 +26,27 @@ job-defaults:
               path: /builds/worker/artifacts/
               type: directory
     run:
         using: mozharness
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         mozconfig-variant: null
         tooltool-downloads: internal
-    toolchains:
-        - android-gradle-dependencies
-        - android-ndk-linux
-        - android-sdk-linux
-        - linux64-clang
-        - linux64-rust-android
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - android-gradle-dependencies
+            - android-ndk-linux
+            - android-sdk-linux
+            - linux64-clang
+            - linux64-rust-android
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 android-api-16/debug:
     description: "Android 4.0 api-16+ Debug"
     index:
         job-name: android-api-16-debug
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -54,18 +55,19 @@ android-api-16/debug:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: api-16-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-x86/opt:
     description: "Android 4.2 x86 Opt"
     index:
         job-name: android-x86-opt
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -74,36 +76,38 @@ android-x86/opt:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-x86-fuzzing/debug:
     description: "Android x86 Fuzzing Debug"
     index:
         job-name: android-x86-fuzzing-debug
     treeherder:
         platform: android-4-2-x86/debug
         symbol: Bf
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86-fuzzing-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-x86-nightly/opt:
     description: "Android 4.2 x86 Nightly"
     attributes:
         enable-full-crashsymbols: true
         nightly: true
     shipping-phase: build
     shipping-product: fennec
@@ -136,18 +140,19 @@ android-api-16/opt:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: api-16
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-api-16/pgo:
     description: "Android 4.0 api-16+ PGO"
     use-pgo: true
     index:
         job-name: android-api-16-pgo
     attributes:
         enable-full-crashsymbols: true
@@ -175,18 +180,19 @@ android-api-16-without-google-play-servi
         env:
             PERFHERDER_EXTRA_OPTIONS: android-api-16-without-google-play-services
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: api-16-without-google-play-services
     run-on-projects: ['mozilla-central']
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-api-16-nightly/opt:
     description: "Android 4.0 api-16+ Nightly"
     use-pgo: android-api-16/pgo
     attributes:
         enable-full-crashsymbols: true
         nightly: true
     shipping-phase: build
@@ -220,18 +226,19 @@ android-aarch64/opt:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: aarch64
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-aarch64/pgo:
     description: "Android 5.0 AArch64 PGO"
     use-pgo: android-api-16/pgo
     index:
         job-name: android-aarch64-pgo
     attributes:
         enable-full-crashsymbols: true
@@ -259,18 +266,19 @@ android-aarch64/debug:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: aarch64-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-aarch64-nightly/opt:
     description: "Android 5.0 AArch64 Nightly"
     use-pgo: android-api-16/pgo
     attributes:
         enable-full-crashsymbols: true
         nightly: true
     shipping-phase: build
@@ -304,18 +312,19 @@ android-x86_64/opt:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86_64
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-x86_64-nightly/opt:
     description: "Android 5.0 x86-64 Nightly"
     attributes:
         enable-full-crashsymbols: true
         nightly: true
     shipping-phase: build
     shipping-product: fennec
@@ -348,18 +357,19 @@ android-x86_64/debug:
     worker-type: b-linux
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86_64-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 
 android-api-16-gcp/debug:
     description: "Android 4.0 api-16+ Debug - built on GCP"
     index:
         job-name: android-api-16-gcp-debug
     attributes:
         enable-full-crashsymbols: true
@@ -371,18 +381,19 @@ android-api-16-gcp/debug:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: api-16-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 
 android-x86-gcp/opt:
     description: "Android 4.2 x86 Opt - built on GCP"
     index:
         job-name: android-x86-gcp-opt
     attributes:
         enable-full-crashsymbols: true
@@ -394,18 +405,19 @@ android-x86-gcp/opt:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-api-16-gcp/opt:
     description: "Android 4.0 api-16+ Opt - built on GCP"
     index:
         job-name: android-api-16-gcp-opt
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -416,18 +428,19 @@ android-api-16-gcp/opt:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: api-16
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-aarch64-gcp/opt:
     description: "Android 5.0 AArch64 Opt - built on GCP"
     index:
         job-name: android-aarch64-gcp-opt
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -438,18 +451,19 @@ android-aarch64-gcp/opt:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: aarch64
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-aarch64-gcp/debug:
     description: "Android 5.0 AArch64 Debug - built on GCP"
     index:
         job-name: android-aarch64-gcp-debug
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -460,18 +474,19 @@ android-aarch64-gcp/debug:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: aarch64-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-x86_64-gcp/opt:
     description: "Android 5.0 x86-64 Opt - built on GCP"
     index:
         job-name: android-x86_64-gcp-opt
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -482,18 +497,19 @@ android-x86_64-gcp/opt:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86_64
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache
 
 android-x86_64-gcp/debug:
     description: "Android 5.0 x86-64 Debug - built on GCP"
     index:
         job-name: android-x86_64-gcp-debug
     attributes:
         enable-full-crashsymbols: true
     treeherder:
@@ -504,10 +520,11 @@ android-x86_64-gcp/debug:
     worker:
         env:
             TOOLTOOL_MANIFEST: "mobile/android/config/tooltool-manifests/android-x86/releng.manifest"
             PERFHERDER_EXTRA_OPTIONS: gcp
     run:
         actions: [get-secrets, build]
         config: ["builds/releng_base_android_64_builds.py"]
         custom-build-variant-cfg: x86_64-debug
-    toolchains:
-        - linux64-sccache
+    fetches:
+        toolchain:
+            - linux64-sccache

--- a/taskcluster/ci/build/kind.yml
+++ b/taskcluster/ci/build/kind.yml
@@ -8,17 +8,16 @@ kind-dependencies:
     - toolchain
     - fetch
     - generate-profile
 
 transforms:
     - taskgraph.transforms.build:transforms
     - taskgraph.transforms.build_attrs:transforms
     - taskgraph.transforms.build_lints:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 jobs-from:
     - android.yml
     - android-stuff.yml
     - linux.yml
     - macosx.yml

--- a/taskcluster/ci/build/linux.yml
+++ b/taskcluster/ci/build/linux.yml
@@ -21,25 +21,26 @@ linux64/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-plain/opt:
     description: "Linux64 Opt Plain"
     index:
         product: firefox
         job-name: linux64-plain-opt
     treeherder:
         platform: linux64/opt
@@ -58,23 +59,24 @@ linux64-plain/opt:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: mozharness/scripts/fx_desktop_build.py
         tooltool-downloads: public
         extra-config:
             disable_package_metrics: true
         mozconfig-variant: plain-opt
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-nasm
-        - linux64-node
-        - linux64-cbindgen
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-nasm
+            - linux64-node
+            - linux64-cbindgen
 
 linux64-fuzzing/debug:
     description: "Linux64 Fuzzing Debug"
     index:
         product: firefox
         job-name: linux64-fuzzing-debug
     treeherder:
         platform: linux64/debug
@@ -92,25 +94,26 @@ linux64-fuzzing/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: fuzzing-debug
         mozconfig-variant: debug-fuzzing
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-clang
-        - linux64-gcc
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-clang
+            - linux64-gcc
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-nasm
+            - linux64-node
 
 linux64/debug:
     description: "Linux64 Debug"
     index:
         product: firefox
         job-name: linux64-debug
     attributes:
         enable-full-crashsymbols: true
@@ -127,25 +130,26 @@ linux64/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: debug
         mozconfig-variant: debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-nasm
+            - linux64-node
 
 linux64-plain/debug:
     description: "Linux64 Debug Plain"
     index:
         product: firefox
         job-name: linux64-plain-debug
     treeherder:
         platform: linux64/debug
@@ -164,23 +168,24 @@ linux64-plain/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         extra-config:
             disable_package_metrics: true
         mozconfig-variant: plain-debug
         script: mozharness/scripts/fx_desktop_build.py
         tooltool-downloads: public
     run-on-projects: [trunk]
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-nasm
-        - linux64-node
-        - linux64-cbindgen
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-nasm
+            - linux64-node
+            - linux64-cbindgen
 
 linux64-devedition-nightly/opt:
     description: "Linux64 devedition Nightly"
     use-pgo: linux64-shippable/opt
     attributes:
         nightly: true
         enable-full-crashsymbols: true
     shipping-phase: build
@@ -205,24 +210,25 @@ linux64-devedition-nightly/opt:
         extra-config:
             stage_platform: 'linux64-devedition'
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
         mozconfig-variant: devedition
     run-on-projects: ['mozilla-beta']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 linux64-base-toolchains/opt:
     description: "Linux64 base toolchains Opt"
     index:
         product: firefox
         job-name: linux64-base-toolchains-opt
     treeherder:
         platform: linux64/opt
@@ -239,24 +245,25 @@ linux64-base-toolchains/opt:
         actions: [get-secrets, build, check-test]
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-clang-4.0
-        - linux64-gcc-6
-        - linux64-rust-1.36
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm-2.13.02
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-clang-4.0
+            - linux64-gcc-6
+            - linux64-rust-1.36
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm-2.13.02
+            - linux64-node
 
 linux64-base-toolchains/debug:
     description: "Linux64 base toolchains Debug"
     index:
         product: firefox
         job-name: linux64-base-toolchains-debug
     treeherder:
         platform: linux64/debug
@@ -275,24 +282,25 @@ linux64-base-toolchains/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: debug
         mozconfig-variant: debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-clang-4.0
-        - linux64-gcc-6
-        - linux64-rust-1.36
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm-2.13.02
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-clang-4.0
+            - linux64-gcc-6
+            - linux64-rust-1.36
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm-2.13.02
+            - linux64-node
 
 linux64-base-toolchains-clang/opt:
     description: "Linux64 base toolchains clang Opt"
     index:
         product: firefox
         job-name: linux64-base-toolchains-clang-opt
     treeherder:
         platform: linux64/opt
@@ -308,23 +316,24 @@ linux64-base-toolchains-clang/opt:
         actions: [get-secrets, build, check-test]
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang-4.0
-        - linux64-rust-1.36
-        - linux64-cbindgen
-        - linux64-nasm-2.13.02
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang-4.0
+            - linux64-rust-1.36
+            - linux64-cbindgen
+            - linux64-nasm-2.13.02
+            - linux64-node
 
 linux64-base-toolchains-clang/debug:
     description: "Linux64 base toolchains clang Debug"
     index:
         product: firefox
         job-name: linux64-base-toolchains-clang-debug
     treeherder:
         platform: linux64/debug
@@ -342,23 +351,24 @@ linux64-base-toolchains-clang/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: debug
         mozconfig-variant: debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang-4.0
-        - linux64-rust-1.36
-        - linux64-cbindgen
-        - linux64-nasm-2.13.02
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang-4.0
+            - linux64-rust-1.36
+            - linux64-cbindgen
+            - linux64-nasm-2.13.02
+            - linux64-node
 
 linux/opt:
     description: "Linux32 Opt"
     index:
         product: firefox
         job-name: linux-opt
     attributes:
         enable-full-crashsymbols: true
@@ -375,25 +385,26 @@ linux/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_32_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux/debug:
     description: "Linux32 Debug"
     index:
         product: firefox
         job-name: linux-debug
     attributes:
         enable-full-crashsymbols: true
@@ -411,25 +422,26 @@ linux/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_32_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: debug
         mozconfig-variant: debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux-rusttests/opt:
     description: "Linux32 Rust Tests Opt"
     index:
         product: firefox
         job-name: linux-rusttests-opt
     treeherder:
         platform: linux32/opt
@@ -450,24 +462,25 @@ linux-rusttests/opt:
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: rusttests
         mozconfig-variant: rusttests
         tooltool-downloads: public
         keep-artifacts: false
         need-xvfb: true
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux-rusttests/debug:
     description: "Linux32 Rust Tests Debug"
     index:
         product: firefox
         job-name: linux-rusttests-debug
     treeherder:
         platform: linux32/debug
@@ -488,24 +501,25 @@ linux-rusttests/debug:
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: rusttests-debug
         mozconfig-variant: rusttests-debug
         tooltool-downloads: public
         keep-artifacts: false
         need-xvfb: true
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux-devedition-nightly/opt:
     description: "Linux32 devedition Nightly"
     use-pgo: linux-shippable/opt
     attributes:
         nightly: true
         enable-full-crashsymbols: true
     shipping-phase: build
@@ -531,24 +545,25 @@ linux-devedition-nightly/opt:
         extra-config:
             stage_platform: linux-devedition
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
         mozconfig-variant: devedition
     run-on-projects: ['mozilla-beta']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 linux-shippable/opt:
     description: "Linux32 Shippable"
     use-pgo: true
     attributes:
         shippable: true
         enable-full-crashsymbols: true
     shipping-phase: build
@@ -570,24 +585,25 @@ linux-shippable/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_32_builds.py
             - taskcluster_nightly.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 linux64-asan/opt:
     description: "Linux64 Opt ASAN"
     index:
         product: firefox
         job-name: linux64-asan-opt
     treeherder:
         platform: linux64/asan
@@ -605,25 +621,26 @@ linux64-asan/opt:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: asan-tc
         mozconfig-variant: nightly-asan
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-asan-fuzzing/opt:
     description: "Linux64 Fuzzing Opt ASAN"
     index:
         product: firefox
         job-name: linux64-fuzzing-asan-opt
     treeherder:
         platform: linux64/asan
@@ -641,25 +658,26 @@ linux64-asan-fuzzing/opt:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: fuzzing-asan-tc
         mozconfig-variant: nightly-fuzzing-asan
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-asan-fuzzing-ccov/opt:
     description: "Linux64 Fuzzing Opt ASAN w/ Coverage"
     index:
         product: firefox
         job-name: linux64-ccov-fuzzing-asan-opt
     treeherder:
         platform: linux64/asan
@@ -677,25 +695,26 @@ linux64-asan-fuzzing-ccov/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         mozconfig-variant: asan-fuzzing-ccov
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-fuzzing-ccov/opt:
     description: "Linux64 Fuzzing Opt w/ Coverage"
     index:
         product: firefox
         job-name: linux64-ccov-fuzzing-opt
     treeherder:
         platform: linux64/opt
@@ -714,25 +733,26 @@ linux64-fuzzing-ccov/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         mozconfig-variant: fuzzing-ccov
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-clang
-        - linux64-gcc
-        - linux64-cbindgen
-        - linux64-rust-nightly
-        - linux64-rust-size
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-clang
+            - linux64-gcc
+            - linux64-cbindgen
+            - linux64-rust-nightly
+            - linux64-rust-size
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-asan-reporter-nightly/opt:
     description: "Linux64 Opt ASAN Reporter Nightly"
     attributes:
         nightly: true
     shipping-product:
         by-release-type:
             nightly: firefox
@@ -761,24 +781,25 @@ linux64-asan-reporter-nightly/opt:
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: asan-reporter-tc
         mozconfig-variant: nightly-asan-reporter
         tooltool-downloads: public
         need-xvfb: true
         mar-channel-id:
             firefox-mozilla-central-asan
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 linux64-asan/debug:
     description: "Linux64 Debug ASAN"
     index:
         product: firefox
         job-name: linux64-asan-debug
     treeherder:
         platform: linux64/asan
@@ -796,25 +817,26 @@ linux64-asan/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: asan-tc-and-debug
         mozconfig-variant: debug-asan
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-shippable/opt:
     description: "Linux64 Shippable"
     use-pgo: true
     attributes:
         shippable: true
         enable-full-crashsymbols: true
     shipping-phase: build
@@ -835,24 +857,25 @@ linux64-shippable/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
             - taskcluster_nightly.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 linux64-noopt/debug:
     description: "Linux64 No-optimize Debug"
     index:
         product: firefox
         job-name: linux64-noopt-debug
     treeherder:
         platform: linux64-noopt/debug
@@ -872,25 +895,26 @@ linux64-noopt/debug:
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: noopt-debug
         mozconfig-variant: noopt-debug
         tooltool-downloads: public
         keep-artifacts: false
         need-xvfb: true
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-rusttests/opt:
     description: "Linux64 Rust Tests Opt"
     index:
         product: firefox
         job-name: linux64-rusttests-opt
     treeherder:
         platform: linux64/opt
@@ -910,24 +934,25 @@ linux64-rusttests/opt:
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: rusttests
         mozconfig-variant: rusttests
         tooltool-downloads: public
         keep-artifacts: false
         need-xvfb: true
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-rusttests/debug:
     description: "Linux64 Rust Tests Debug"
     index:
         product: firefox
         job-name: linux64-rusttests-debug
     treeherder:
         platform: linux64/debug
@@ -947,24 +972,25 @@ linux64-rusttests/debug:
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: rusttests-debug
         mozconfig-variant: rusttests-debug
         tooltool-downloads: public
         keep-artifacts: false
         need-xvfb: true
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-tup/opt:
     description: "Linux64 Tup"
     index:
         product: firefox
         job-name: linux64-tup-opt
     treeherder:
         platform: linux64/opt
@@ -983,25 +1009,26 @@ linux64-tup/opt:
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: tup
         mozconfig-variant: tup
         tooltool-downloads: public
         need-xvfb: true
     run-on-projects: []
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust-nightly
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-tup
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust-nightly
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-tup
+            - linux64-nasm
+            - linux64-node
 
 linux64-ccov/debug:
     description: "Linux64-CCov Debug"
     index:
         product: firefox
         job-name: linux64-ccov-debug
     treeherder:
         platform: linux64-ccov/debug
@@ -1024,27 +1051,26 @@ linux64-ccov/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: code-coverage-debug
         mozconfig-variant: code-coverage-debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-clang-8
-        - linux64-rust-nightly
-        - linux64-gcc
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
     fetches:
         toolchain:
+            - linux64-clang-8
+            - linux64-rust-nightly
+            - linux64-gcc
             - linux64-grcov
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-ccov/opt:
     description: "Linux64-CCov Opt"
     index:
         product: firefox
         job-name: linux64-ccov-opt
     treeherder:
         platform: linux64-ccov/opt
@@ -1063,24 +1089,25 @@ linux64-ccov/opt:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: code-coverage-opt
         mozconfig-variant: code-coverage-opt
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-clang-8
-        - linux64-rust-nightly
-        - linux64-gcc
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-clang-8
+            - linux64-rust-nightly
+            - linux64-gcc
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-add-on-devel/opt:
     description: "Linux64 add-on-devel"
     index:
         product: firefox
         job-name: linux64-add-on-devel
     treeherder:
         platform: linux64-add-on-devel/opt
@@ -1097,25 +1124,26 @@ linux64-add-on-devel/opt:
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: add-on-devel
         mozconfig-variant: add-on-devel
         tooltool-downloads: public
         need-xvfb: true
     run-on-projects: ['mozilla-beta', 'mozilla-release', 'mozilla-esr45']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-aarch64/opt:
     description: "Linux64 aarch64 Opt"
     index:
         product: firefox
         job-name: linux64-aarch64-opt
     attributes:
         enable-full-crashsymbols: true
@@ -1135,24 +1163,25 @@ linux64-aarch64/opt:
             - builds/releng_base_linux_64_builds.py
         extra-config:
             mozconfig_platform: linux64-aarch64
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         mozconfig-variant: opt
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-node
 
 linux-gcp/debug:
     description: "Linux32 Debug - built on GCP"
     index:
         product: firefox
         job-name: linux-gcp-debug
     attributes:
         enable-full-crashsymbols: true
@@ -1173,25 +1202,26 @@ linux-gcp/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_32_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: debug
         mozconfig-variant: debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux-gcp/opt:
     description: "Linux32 Opt - built on GCP"
     index:
         product: firefox
         job-name: linux-gcp-opt
     attributes:
         enable-full-crashsymbols: true
@@ -1211,25 +1241,26 @@ linux-gcp/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_32_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 linux64-gcp/debug:
     description: "Linux64 Debug - built on GCP"
     index:
         product: firefox
         job-name: linux64-gcp-debug
     attributes:
         enable-full-crashsymbols: true
@@ -1249,25 +1280,26 @@ linux64-gcp/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: debug
         mozconfig-variant: debug
         tooltool-downloads: public
         need-xvfb: true
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-nasm
+            - linux64-node
 
 linux64-gcp/opt:
     description: "Linux64 Opt - built on GCP"
     index:
         product: firefox
         job-name: linux64-gcp-opt
     attributes:
         enable-full-crashsymbols: true
@@ -1286,17 +1318,18 @@ linux64-gcp/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_linux_64_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: public
         need-xvfb: true
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-clang
-        - linux64-rust
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-clang
+            - linux64-rust
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node

--- a/taskcluster/ci/build/macosx.yml
+++ b/taskcluster/ci/build/macosx.yml
@@ -24,29 +24,30 @@ macosx64/debug:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: cross-debug
         mozconfig-variant: debug
         tooltool-downloads: internal
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64/opt:
     description: "MacOS X x64 Cross-compile"
     index:
         product: firefox
         job-name: macosx64-opt
     attributes:
         enable-full-crashsymbols: true
@@ -64,29 +65,30 @@ macosx64/opt:
         actions: [get-secrets, build]
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: internal
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-asan-fuzzing/opt:
     description: "MacOS X x64 Cross-compile Fuzzing ASAN"
     index:
         product: firefox
         job-name: macosx64-fuzzing-asan-opt
     treeherder:
         platform: osx-cross/asan
@@ -103,29 +105,30 @@ macosx64-asan-fuzzing/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: cross-fuzzing-asan
         mozconfig-variant: nightly-fuzzing-asan
         tooltool-downloads: internal
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-fuzzing/debug:
     description: "MacOS X x64 Cross-compile Fuzzing Debug"
     index:
         product: firefox
         job-name: macosx64-fuzzing-debug
     attributes:
         enable-full-crashsymbols: true
@@ -144,29 +147,30 @@ macosx64-fuzzing/debug:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: cross-fuzzing-debug
         mozconfig-variant: debug-fuzzing
         tooltool-downloads: internal
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-devedition-nightly/opt:
     description: "MacOS X Dev Edition x64 Nightly"
     attributes:
         nightly: true
         enable-full-crashsymbols: true
     shipping-phase: build
     shipping-product: devedition
@@ -192,28 +196,29 @@ macosx64-devedition-nightly/opt:
             - taskcluster_nightly.py
         extra-config:
             stage_platform: macosx64-devedition
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: internal
         mozconfig-variant: devedition
     run-on-projects: ['mozilla-beta']
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 macosx64-noopt/debug:
     description: "MacOS X x64 No-optimize Debug"
     index:
         product: firefox
         job-name: macosx64-noopt-debug
     treeherder:
         platform: osx-cross-noopt/debug
@@ -232,29 +237,30 @@ macosx64-noopt/debug:
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: cross-noopt-debug
         mozconfig-variant: cross-noopt-debug
         tooltool-downloads: internal
         keep-artifacts: false
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-add-on-devel/opt:
     description: "MacOS X x64 add-on-devel"
     index:
         product: firefox
         job-name: macosx64-add-on-devel
     treeherder:
         platform: osx-cross-add-on-devel/opt
@@ -272,29 +278,30 @@ macosx64-add-on-devel/opt:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: add-on-devel
         mozconfig-variant: add-on-devel
         tooltool-downloads: internal
     run-on-projects: ['mozilla-beta', 'mozilla-release', 'mozilla-esr45']
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-shippable/opt:
     description: "MacOS X x64 Cross-compile"
     attributes:
         shippable: true
         enable-full-crashsymbols: true
     shipping-phase: build
     shipping-product: firefox
@@ -316,28 +323,29 @@ macosx64-shippable/opt:
         actions: [get-secrets, build]
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
             - taskcluster_nightly.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: internal
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
 
 macosx64-ccov/debug:
     description: "MacOS X x64 Cross-compile Code Coverage"
     index:
         product: firefox
         job-name: macosx64-ccov-debug
     treeherder:
         platform: osx-cross-ccov/debug
@@ -355,29 +363,30 @@ macosx64-ccov/debug:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: code-coverage-debug
         mozconfig-variant: code-coverage-debug
         tooltool-downloads: internal
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-nightly-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-nightly-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-gcp/debug:
     description: "MacOS X x64 Cross-compile - built on GCP"
     index:
         product: firefox
         job-name: macosx64-gcp-debug
     attributes:
         enable-full-crashsymbols: true
@@ -397,29 +406,30 @@ macosx64-gcp/debug:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         custom-build-variant-cfg: cross-debug
         mozconfig-variant: debug
         tooltool-downloads: internal
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node
 
 macosx64-gcp/opt:
     description: "MacOS X x64 Cross-compile - built on GCP"
     index:
         product: firefox
         job-name: macosx64-gcp-opt
     attributes:
         enable-full-crashsymbols: true
@@ -438,21 +448,22 @@ macosx64-gcp/opt:
         actions: [get-secrets, build]
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_mac_64_cross_builds.py
         script: "mozharness/scripts/fx_desktop_build.py"
         secrets: true
         tooltool-downloads: internal
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - linux64-binutils
-        - linux64-cctools-port
-        - linux64-clang-macosx-cross
-        - linux64-hfsplus
-        - linux64-libdmg
-        - linux64-llvm-dsymutil
-        - linux64-rust-macos
-        - linux64-rust-size
-        - linux64-cbindgen
-        - linux64-sccache
-        - linux64-nasm
-        - linux64-node
+    fetches:
+        toolchain:
+            - linux64-binutils
+            - linux64-cctools-port
+            - linux64-clang-macosx-cross
+            - linux64-hfsplus
+            - linux64-libdmg
+            - linux64-llvm-dsymutil
+            - linux64-rust-macos
+            - linux64-rust-size
+            - linux64-cbindgen
+            - linux64-sccache
+            - linux64-nasm
+            - linux64-node

--- a/taskcluster/ci/build/windows-mingw.yml
+++ b/taskcluster/ci/build/windows-mingw.yml
@@ -26,27 +26,28 @@ win32-mingwclang/opt:
         env:
             PERFHERDER_EXTRA_OPTIONS: "opt 32 clang"
     run:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_windows_32_mingw_builds.py
             - builds/releng_sub_windows_configs/32_mingwclang.py
         mozconfig-variant: mingwclang
-    toolchains:
-        - mingw32-rust
-        - linux64-upx
-        - linux64-wine
-        - linux64-sccache
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
-        - linux64-clang-mingw-x86
-        - linux64-mingw32-nsis
-        - linux64-mingw-fxc2-x86
+    fetches:
+        toolchain:
+            - mingw32-rust
+            - linux64-upx
+            - linux64-wine
+            - linux64-sccache
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
+            - linux64-clang-mingw-x86
+            - linux64-mingw32-nsis
+            - linux64-mingw-fxc2-x86
 
 win32-mingwclang/debug:
     description: "Win32 MinGW-Clang Debug"
     index:
         product: firefox
         job-name: win32-mingwclang-debug
     treeherder:
         platform: windows-mingw32/all
@@ -56,27 +57,28 @@ win32-mingwclang/debug:
         env:
             PERFHERDER_EXTRA_OPTIONS: "debug 32 clang"
     run:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_windows_32_mingw_builds.py
             - builds/releng_sub_windows_configs/32_mingwclang.py
         mozconfig-variant: mingwclang-debug
-    toolchains:
-        - mingw32-rust
-        - linux64-upx
-        - linux64-wine
-        - linux64-sccache
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
-        - linux64-clang-mingw-x86
-        - linux64-mingw32-nsis
-        - linux64-mingw-fxc2-x86
+    fetches:
+        toolchain:
+            - mingw32-rust
+            - linux64-upx
+            - linux64-wine
+            - linux64-sccache
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
+            - linux64-clang-mingw-x86
+            - linux64-mingw32-nsis
+            - linux64-mingw-fxc2-x86
 
 win64-mingwclang/opt:
     description: "Win64 MinGW-Clang Opt"
     index:
         product: firefox
         job-name: win64-mingwclang-opt
     treeherder:
         platform: windows-mingw32/all
@@ -86,27 +88,28 @@ win64-mingwclang/opt:
         env:
             PERFHERDER_EXTRA_OPTIONS: "opt 64 clang"
     run:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_windows_64_mingw_builds.py
             - builds/releng_sub_windows_configs/64_mingwclang.py
         mozconfig-variant: mingwclang
-    toolchains:
-        - mingw32-rust
-        - linux64-upx
-        - linux64-wine
-        - linux64-sccache
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
-        - linux64-clang-mingw-x64
-        - linux64-mingw32-nsis
-        - linux64-mingw-fxc2-x86
+    fetches:
+        toolchain:
+            - mingw32-rust
+            - linux64-upx
+            - linux64-wine
+            - linux64-sccache
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
+            - linux64-clang-mingw-x64
+            - linux64-mingw32-nsis
+            - linux64-mingw-fxc2-x86
 
 win64-mingwclang/debug:
     description: "Win64 MinGW-Clang Debug"
     index:
         product: firefox
         job-name: win64-mingwclang-debug
     treeherder:
         platform: windows-mingw32/all
@@ -116,19 +119,20 @@ win64-mingwclang/debug:
         env:
             PERFHERDER_EXTRA_OPTIONS: "debug 64 clang"
     run:
         config:
             - builds/releng_base_firefox.py
             - builds/releng_base_windows_64_mingw_builds.py
             - builds/releng_sub_windows_configs/64_mingwclang.py
         mozconfig-variant: mingwclang-debug
-    toolchains:
-        - mingw32-rust
-        - linux64-upx
-        - linux64-wine
-        - linux64-sccache
-        - linux64-cbindgen
-        - linux64-nasm
-        - linux64-node
-        - linux64-clang-mingw-x64
-        - linux64-mingw32-nsis
-        - linux64-mingw-fxc2-x86
+    fetches:
+        toolchain:
+            - mingw32-rust
+            - linux64-upx
+            - linux64-wine
+            - linux64-sccache
+            - linux64-cbindgen
+            - linux64-nasm
+            - linux64-node
+            - linux64-clang-mingw-x64
+            - linux64-mingw32-nsis
+            - linux64-mingw-fxc2-x86

--- a/taskcluster/ci/build/windows.yml
+++ b/taskcluster/ci/build/windows.yml
@@ -28,24 +28,25 @@ win32/debug:
         script: mozharness/scripts/fx_desktop_build.py
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
             - builds/taskcluster_sub_win32/debug.py
         mozconfig-variant: debug
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win32/opt:
     description: "Win32 Opt"
     index:
         product: firefox
         job-name: win32-opt
     attributes:
         enable-full-crashsymbols: true
@@ -64,24 +65,25 @@ win32/opt:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
         extra-config:
             stage_platform: win32
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64/debug:
     description: "Win64 Debug"
     index:
         product: firefox
         job-name: win64-debug
     attributes:
         enable-full-crashsymbols: true
@@ -99,24 +101,25 @@ win64/debug:
         script: mozharness/scripts/fx_desktop_build.py
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/debug.py
         mozconfig-variant: debug
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-fuzzing/debug:
     description: "Win64 Fuzzing Debug"
     index:
         product: firefox
         job-name: win64-fuzzing-debug
     attributes:
         enable-full-crashsymbols: true
@@ -136,24 +139,25 @@ win64-fuzzing/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/debug.py
         mozconfig-variant: debug-fuzzing
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-plain/debug:
     description: "Win64 Debug Plain"
     index:
         product: firefox
         job-name: win64-plain-debug
     treeherder:
         platform: windows2012-64/debug
@@ -173,22 +177,23 @@ win64-plain/debug:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             disable_package_metrics: true
             stage_platform: win64
         mozconfig-variant: plain-debug
     run-on-projects: ['trunk']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-node
-        - win64-nasm
-        - win64-cbindgen
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-node
+            - win64-nasm
+            - win64-cbindgen
 
 win64/opt:
     description: "Win64 Opt"
     index:
         product: firefox
         job-name: win64-opt
     attributes:
         enable-full-crashsymbols: true
@@ -207,24 +212,25 @@ win64/opt:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             stage_platform: win64
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-plain/opt:
     description: "Win64 Opt Plain"
     index:
         product: firefox
         job-name: win64-plain-opt
     treeherder:
         platform: windows2012-64/opt
@@ -244,22 +250,23 @@ win64-plain/opt:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             disable_package_metrics: true
             stage_platform: win64
         mozconfig-variant: plain-opt
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-nasm
-        - win64-node
-        - win64-cbindgen
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-nasm
+            - win64-node
+            - win64-cbindgen
 
 win32-shippable/opt:
     description: "Win32 Opt Shippable"
     use-pgo: true
     index:
         product: firefox
         job-name: win32-opt
         type: shippable
@@ -294,23 +301,24 @@ win32-shippable/opt:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win32
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node
 
 win64-shippable/opt:
     description: "Win64 Shippable"
     use-pgo: true
     index:
         product: firefox
         job-name: win64-opt
         type: shippable
@@ -334,23 +342,24 @@ win64-shippable/opt:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win64
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node
 
 win32-add-on-devel/opt:
     description: "Windows32 add-on-devel"
     index:
         product: firefox
         job-name: win32-add-on-devel
     treeherder:
         platform: windows2012-32-add-on-devel/opt
@@ -368,24 +377,25 @@ win32-add-on-devel/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
         extra-config:
             stage_platform: win32-add-on-devel
         mozconfig-variant: add-on-devel
     run-on-projects: ['mozilla-beta', 'mozilla-release']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-add-on-devel/opt:
     description: "Windows64 add-on-devel"
     index:
         product: firefox
         job-name: win64-add-on-devel
     treeherder:
         platform: windows2012-64-add-on-devel/opt
@@ -403,24 +413,25 @@ win64-add-on-devel/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             stage_platform: win64-on-devel
         mozconfig-variant: add-on-devel
     run-on-projects: ['mozilla-beta', 'mozilla-release']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-noopt/debug:
     description: "Win64 No-optimize Debug"
     index:
         product: firefox
         job-name: win64-noopt-debug
     treeherder:
         platform: windows2012-64-noopt/debug
@@ -437,24 +448,25 @@ win64-noopt/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/noopt_debug.py
         mozconfig-variant: noopt-debug
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win32-noopt/debug:
     description: "Win32 No-optimize Debug"
     index:
         product: firefox
         job-name: win32-noopt-debug
     treeherder:
         platform: windows2012-32-noopt/debug
@@ -471,24 +483,25 @@ win32-noopt/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
             - builds/taskcluster_sub_win32/noopt_debug.py
         mozconfig-variant: noopt-debug
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win32-rusttests/opt:
     description: "Win32 Rust Tests Opt"
     index:
         product: firefox
         job-name: win32-rusttests-opt
     treeherder:
         platform: windows2012-32/opt
@@ -510,23 +523,24 @@ win32-rusttests/opt:
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
         extra-config:
             stage_platform: win32-rusttests
             build_targets: ['pre-export', 'export', 'recurse_rusttests']
             disable_package_metrics: true
         mozconfig-variant: rusttests
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win32-rusttests/debug:
     description: "Win32 Rust Tests Debug"
     index:
         product: firefox
         job-name: win32-rusttests-debug
     treeherder:
         platform: windows2012-32/debug
@@ -548,23 +562,24 @@ win32-rusttests/debug:
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
         extra-config:
             stage_platform: win32-rusttests
             build_targets: ['pre-export', 'export', 'recurse_rusttests']
             disable_package_metrics: true
         mozconfig-variant: rusttests-debug
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-rusttests/opt:
     description: "Win64 Rust Tests Opt"
     index:
         product: firefox
         job-name: win64-rusttests-opt
     treeherder:
         platform: windows2012-64/opt
@@ -583,23 +598,24 @@ win64-rusttests/opt:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/rusttests_opt.py
         mozconfig-variant: rusttests
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-rusttests/debug:
     description: "Win64 Rust Tests Debug"
     index:
         product: firefox
         job-name: win64-rusttests-debug
     treeherder:
         platform: windows2012-64/debug
@@ -618,23 +634,24 @@ win64-rusttests/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/rusttests_opt.py
         mozconfig-variant: rusttests-debug
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-ccov/debug:
     description: "Win64 Debug Code Coverage"
     index:
         product: firefox
         job-name: win64-ccov-debug
     treeherder:
         platform: windows2012-64/ccov
@@ -655,27 +672,26 @@ win64-ccov/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/ccov_debug.py
         mozconfig-variant: code-coverage
     run-on-projects: ['mozilla-central', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust-nightly
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
     fetches:
         toolchain:
+            - win64-clang-cl
+            - win64-rust-nightly
+            - win64-rust-size
+            - win64-cbindgen
             - win64-grcov
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-asan/debug:
     description: "Win64 Debug ASAN"
     index:
         product: firefox
         job-name: win64-asan-debug
     treeherder:
         platform: windows2012-64/asan
@@ -693,24 +709,25 @@ win64-asan/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - builds/taskcluster_sub_win64/asan_debug.py
         mozconfig-variant: debug-asan
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-asan/opt:
     description: "Win64 Opt ASAN"
     index:
         product: firefox
         job-name: win64-asan-opt
     treeherder:
         platform: windows2012-64/asan
@@ -729,24 +746,25 @@ win64-asan/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             stage_platform: win64-asan
         mozconfig-variant: nightly-asan
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-asan-reporter-nightly/opt:
     description: "Win64 Opt ASAN Reporter Nightly"
     attributes:
         nightly: true
     shipping-product:
         by-release-type:
             nightly: firefox
@@ -775,23 +793,24 @@ win64-asan-reporter-nightly/opt:
             - builds/taskcluster_sub_win64/asan_reporter_opt.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win64-asan-reporter
         mozconfig-variant: nightly-asan-reporter
         mar-channel-id:
             firefox-mozilla-central-asan
     run-on-projects: ['mozilla-central']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node
 
 win64-asan-fuzzing/opt:
     description: "Win64 Fuzzing Opt ASAN"
     index:
         product: firefox
         job-name: win64-fuzzing-asan-opt
     treeherder:
         platform: windows2012-64/asan
@@ -809,24 +828,25 @@ win64-asan-fuzzing/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             stage_platform: win64-fuzzing-asan
         mozconfig-variant: nightly-fuzzing-asan
     run-on-projects: ['trunk', 'try']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win32-devedition-nightly/opt:
     description: "Win32 Dev Edition Nightly"
     use-pgo: win32-shippable/opt
     index:
         product: devedition
         job-name: win32-opt
         type: nightly
@@ -862,23 +882,24 @@ win32-devedition-nightly/opt:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win32.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win32-devedition
         mozconfig-variant: devedition
     run-on-projects: ['mozilla-beta']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node
 
 win64-devedition-nightly/opt:
     description: "Win64 Dev Edition Nightly"
     use-pgo: win64-shippable/opt
     index:
         product: devedition
         job-name: win64-opt
         type: nightly
@@ -904,23 +925,24 @@ win64-devedition-nightly/opt:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win64-devedition
         mozconfig-variant: devedition
     run-on-projects: ['mozilla-beta']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node
 
 win64-aarch64/debug:
     description: "AArch64 Win64 Debug"
     index:
         product: firefox
         job-name: win64-aarch64-debug
     attributes:
         enable-full-crashsymbols: true
@@ -941,24 +963,25 @@ win64-aarch64/debug:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_sub_win64/debug.py
         extra-config:
             mozconfig_platform: win64-aarch64
         mozconfig-variant: debug
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-aarch64/opt:
     description: "AArch64 Win64 Opt"
     index:
         product: firefox
         job-name: win64-aarch64-opt
     attributes:
         enable-full-crashsymbols: true
@@ -979,24 +1002,25 @@ win64-aarch64/opt:
         secrets: true
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             stage_platform: win64-aarch64
             mozconfig_platform: win64-aarch64
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-sccache
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-sccache
+            - win64-nasm
+            - win64-node
 
 win64-aarch64-eme/opt:
     description: "AArch64 Win64 Opt w/ EME"
     index:
         product: firefox
         job-name: win64-aarch64-eme-opt
     treeherder:
         platform: windows2012-aarch64/opt
@@ -1021,18 +1045,19 @@ win64-aarch64-eme/opt:
             - builds/taskcluster_base_windows.py
             - builds/taskcluster_base_win64.py
         extra-config:
             stage_platform: win64-aarch64
             mozconfig_platform: win64-aarch64
     dependencies:
         win32-opt: build-win32/opt
         win64-aarch64-opt: build-win64-aarch64/opt
-    toolchains:
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-node
 
 win64-aarch64-shippable/opt:
     description: "AArch64 Win64 Shippable"
     index:
         product: firefox
         job-name: win64-aarch64-opt
         type: shippable
     attributes:
@@ -1109,18 +1134,18 @@ win64-aarch64-shippable/opt:
               extract: false
               dest: ../public/build
             - artifact: target.generated-files.tar.gz
               extract: false
               dest: ../public/build
             - artifact: target.langpack.xpi
               extract: false
               dest: ../public/build
-    toolchains:
-        - win64-node
+        toolchain:
+            - win64-node
 
 win64-aarch64-shippable-no-eme/opt:
     description: "AArch64 Win64 Shippable w/o EME"
     use-pgo: win64-shippable/opt
     index:
         product: firefox
         job-name: win64-aarch64-no-eme-opt
         type: shippable
@@ -1146,23 +1171,24 @@ win64-aarch64-shippable-no-eme/opt:
         config:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win64-aarch64
             mozconfig_platform: win64-aarch64
     run-on-projects: []
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node
 
 
 win64-aarch64-devedition-nightly/opt:
     description: "AArch64 Win64 MSVC Devedition Nightly"
     index:
         product: devedition
         job-name: win64-aarch64-opt
         type: nightly
@@ -1190,15 +1216,16 @@ win64-aarch64-devedition-nightly/opt:
             - builds/releng_base_firefox.py
             - builds/taskcluster_base_windows.py
             - taskcluster_nightly.py
         extra-config:
             stage_platform: win64-aarch64
             mozconfig_platform: win64-aarch64
         mozconfig-variant: devedition
     run-on-projects: ['mozilla-beta']
-    toolchains:
-        - win64-clang-cl
-        - win64-rust
-        - win64-rust-size
-        - win64-cbindgen
-        - win64-nasm
-        - win64-node
+    fetches:
+        toolchain:
+            - win64-clang-cl
+            - win64-rust
+            - win64-rust-size
+            - win64-cbindgen
+            - win64-nasm
+            - win64-node

--- a/taskcluster/ci/generate-profile/kind.yml
+++ b/taskcluster/ci/generate-profile/kind.yml
@@ -7,17 +7,16 @@ loader: taskgraph.loader.transform:loade
 kind-dependencies:
     - toolchain
     - instrumented-build
 
 transforms:
     - taskgraph.transforms.build_attrs:transforms
     - taskgraph.transforms.release_deps:transforms
     - taskgraph.transforms.run_pgo_profile:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 
 job-defaults:
     treeherder:
         symbol: Bpgo(run)
         kind: build
@@ -122,18 +121,19 @@ jobs:
             job-script: taskcluster/scripts/tester/test-linux.sh
             script: android_emulator_pgo.py
             tooltool-downloads: internal
             options: [installer-path=/builds/worker/fetches/target.apk]
             config:
                 - android/android_common.py
                 - android/androidarm_4_3.py
                 - android/android_pgo.py
-        toolchains:
-            - linux64-clang
+        fetches:
+            toolchain:
+                - linux64-clang
 
     win32-shippable/opt:
         description: "Win32 Profile Generation"
         shipping-phase: build
         shipping-product: firefox
         index:
             product: firefox
             job-name: win32-profile

--- a/taskcluster/ci/instrumented-build/kind.yml
+++ b/taskcluster/ci/instrumented-build/kind.yml
@@ -7,17 +7,16 @@ loader: taskgraph.loader.transform:loade
 kind-dependencies:
     - toolchain
     - fetch
 
 transforms:
     - taskgraph.transforms.build:transforms
     - taskgraph.transforms.build_attrs:transforms
     - taskgraph.transforms.build_lints:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 job-defaults:
     shipping-phase: build
     treeherder:
         symbol: Bpgo(instr)
         tier: 1
@@ -42,48 +41,50 @@ jobs:
             docker-image: {in-tree: debian7-i386-build}
         run:
             config:
                 - builds/releng_base_firefox.py
                 - builds/releng_base_linux_32_builds.py
             mozconfig-variant: profile-generate
             tooltool-downloads: public
             need-xvfb: true
-        toolchains:
-            - linux64-binutils
-            - linux64-clang
-            - linux64-rust
-            - linux64-rust-size
-            - linux64-cbindgen
-            - linux64-sccache
-            - linux64-nasm
-            - linux64-node
+        fetches:
+            toolchain:
+                - linux64-binutils
+                - linux64-clang
+                - linux64-rust
+                - linux64-rust-size
+                - linux64-cbindgen
+                - linux64-sccache
+                - linux64-nasm
+                - linux64-node
 
     linux64-shippable/opt:
         description: "Linux64 Instrumented"
         shipping-product: firefox
         treeherder:
             platform: linux64-shippable/opt
         worker-type: b-linux
         run:
             config:
                 - builds/releng_base_firefox.py
                 - builds/releng_base_linux_64_builds.py
             mozconfig-variant: profile-generate
             tooltool-downloads: public
             need-xvfb: true
-        toolchains:
-            - linux64-binutils
-            - linux64-clang
-            - linux64-rust
-            - linux64-rust-size
-            - linux64-cbindgen
-            - linux64-sccache
-            - linux64-nasm
-            - linux64-node
+        fetches:
+            toolchain:
+                - linux64-binutils
+                - linux64-clang
+                - linux64-rust
+                - linux64-rust-size
+                - linux64-cbindgen
+                - linux64-sccache
+                - linux64-nasm
+                - linux64-node
 
     android-api-16/pgo:
         description: "Android 4.0 api-16+ PGO instrumented"
         shipping-product: fennec
         treeherder:
             platform: android-4-0-armv7-api16/pgo
         worker-type: b-linux
         worker:
@@ -101,27 +102,28 @@ jobs:
                 - name: public/build/geckoview_example.apk
                   path: /builds/worker/workspace/build/src/obj-firefox/gradle/build/mobile/android/geckoview_example/outputs/apk/withGeckoBinaries/debug/geckoview_example-withGeckoBinaries-debug.apk
                   type: file
         run:
             config:
                 - builds/releng_base_android_64_builds.py
             custom-build-variant-cfg: api-16-profile-generate
             tooltool-downloads: internal
-        toolchains:
-            - android-gradle-dependencies
-            - android-ndk-linux
-            - android-sdk-linux
-            - linux64-clang-android-cross
-            - linux64-rust-android
-            - linux64-rust-size
-            - linux64-cbindgen
-            - linux64-sccache
-            - linux64-nasm
-            - linux64-node
+        fetches:
+            toolchain:
+                - android-gradle-dependencies
+                - android-ndk-linux
+                - android-sdk-linux
+                - linux64-clang-android-cross
+                - linux64-rust-android
+                - linux64-rust-size
+                - linux64-cbindgen
+                - linux64-sccache
+                - linux64-nasm
+                - linux64-node
 
     win32-shippable/opt:
         description: "Win32 Shippable PGO Instrumented"
         shipping-product: firefox
         treeherder:
             platform: windows2012-32-shippable/opt
         worker-type: b-win2012
         worker:
@@ -132,23 +134,24 @@ jobs:
             options: [append-env-variables-from-configs]
             mozconfig-variant: profile-generate
             config:
                 - builds/releng_base_firefox.py
                 - builds/taskcluster_base_windows.py
                 - builds/taskcluster_base_win32.py
             extra-config:
                 stage_platform: win32
-        toolchains:
-            - win64-clang-cl
-            - win64-rust
-            - win64-rust-size
-            - win64-cbindgen
-            - win64-nasm
-            - win64-node
+        fetches:
+            toolchain:
+                - win64-clang-cl
+                - win64-rust
+                - win64-rust-size
+                - win64-cbindgen
+                - win64-nasm
+                - win64-node
 
     win64-shippable/opt:
         description: "Win64 Shippable PGO Instrumented"
         shipping-product: firefox
         treeherder:
             platform: windows2012-64-shippable/opt
         worker-type: b-win2012
         worker:
@@ -159,15 +162,16 @@ jobs:
             options: [append-env-variables-from-configs]
             mozconfig-variant: profile-generate
             config:
                 - builds/releng_base_firefox.py
                 - builds/taskcluster_base_windows.py
                 - builds/taskcluster_base_win64.py
             extra-config:
                 stage_platform: win64
-        toolchains:
-            - win64-clang-cl
-            - win64-rust
-            - win64-rust-size
-            - win64-cbindgen
-            - win64-nasm
-            - win64-node
+        fetches:
+            toolchain:
+                - win64-clang-cl
+                - win64-rust
+                - win64-rust-size
+                - win64-cbindgen
+                - win64-nasm
+                - win64-node

--- a/taskcluster/ci/l10n/kind.yml
+++ b/taskcluster/ci/l10n/kind.yml
@@ -3,17 +3,16 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 ---
 loader: taskgraph.loader.multi_dep:loader
 
 group-by: platform
 
 transforms:
     - taskgraph.transforms.l10n:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 kind-dependencies:
     - build
     - build-signing
     - repackage
     - toolchain
@@ -47,25 +46,26 @@ job-template:
         by-build-platform:
             android-api-16:
                 in-tree: android-build
             default: null
     secrets:
         by-build-platform:
             default: false
             android-api-16: true
-    toolchains:
-        by-build-platform:
-            default: []
-            macosx64.*:
-                - linux64-libdmg
-                - linux64-hfsplus
-            android-api-16:
-                - android-gradle-dependencies
-                - android-sdk-linux
+    fetches:
+        toolchain:
+            by-build-platform:
+                default: []
+                macosx64.*:
+                    - linux64-libdmg
+                    - linux64-hfsplus
+                android-api-16:
+                    - android-gradle-dependencies
+                    - android-sdk-linux
     tooltool:
         by-build-platform:
             default: internal
             linux.*: public
     index:
         type: l10n
         product:
             by-build-platform:

--- a/taskcluster/ci/nightly-l10n/kind.yml
+++ b/taskcluster/ci/nightly-l10n/kind.yml
@@ -3,17 +3,16 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 ---
 loader: taskgraph.loader.multi_dep:loader
 
 group-by: platform
 
 transforms:
     - taskgraph.transforms.l10n:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 kind-dependencies:
     - build
     - build-signing
     - repackage
     - toolchain
@@ -64,25 +63,26 @@ job-template:
         by-build-platform:
             android-api-16-nightly:
                 in-tree: android-build
             default: null
     secrets:
         by-build-platform:
             default: false
             android-api-16-nightly: true
-    toolchains:
-        by-build-platform:
-            default: []
-            macosx64.*:
-                - linux64-libdmg
-                - linux64-hfsplus
-            android-api-16-nightly:
-                - android-gradle-dependencies
-                - android-sdk-linux
+    fetches:
+        toolchain:
+            by-build-platform:
+                default: []
+                macosx64.*:
+                    - linux64-libdmg
+                    - linux64-hfsplus
+                android-api-16-nightly:
+                    - android-gradle-dependencies
+                    - android-sdk-linux
     tooltool:
         by-build-platform:
             default: internal
             linux.*: public
     index:
         type:
             by-build-platform:
                 .*nightly.*: nightly-l10n

--- a/taskcluster/ci/release-eme-free-repack-repackage/kind.yml
+++ b/taskcluster/ci/release-eme-free-repack-repackage/kind.yml
@@ -3,17 +3,16 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 ---
 loader: taskgraph.loader.single_dep:loader
 
 transforms:
     - taskgraph.transforms.chunk_partners:transforms
     - taskgraph.transforms.name_sanity:transforms
     - taskgraph.transforms.repackage_partner:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 kind-dependencies:
     - release-eme-free-repack
     - release-eme-free-repack-signing
     - toolchain
 

--- a/taskcluster/ci/release-partner-repack-repackage/kind.yml
+++ b/taskcluster/ci/release-partner-repack-repackage/kind.yml
@@ -3,17 +3,16 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 ---
 loader: taskgraph.loader.single_dep:loader
 
 transforms:
     - taskgraph.transforms.chunk_partners:transforms
     - taskgraph.transforms.name_sanity:transforms
     - taskgraph.transforms.repackage_partner:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 kind-dependencies:
     - release-partner-repack
     - release-partner-repack-signing
     - toolchain
 

--- a/taskcluster/ci/release-source/kind.yml
+++ b/taskcluster/ci/release-source/kind.yml
@@ -6,17 +6,16 @@ loader: taskgraph.loader.transform:loade
 
 kind-dependencies:
     - toolchain
 
 transforms:
     - taskgraph.transforms.build:transforms
     - taskgraph.transforms.build_attrs:transforms
     - taskgraph.transforms.build_lints:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 
 job-defaults:
     shipping-phase: promote
     treeherder:
         symbol: Src

--- a/taskcluster/ci/repackage-l10n/kind.yml
+++ b/taskcluster/ci/repackage-l10n/kind.yml
@@ -3,17 +3,16 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 ---
 loader: taskgraph.loader.single_dep:loader
 
 transforms:
     - taskgraph.transforms.repackage_l10n:transforms
     - taskgraph.transforms.name_sanity:transforms
     - taskgraph.transforms.repackage:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 kind-dependencies:
     - nightly-l10n-signing
     - toolchain
 
 only-for-build-platforms:

--- a/taskcluster/ci/repackage-msi/kind.yml
+++ b/taskcluster/ci/repackage-msi/kind.yml
@@ -2,17 +2,16 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 ---
 loader: taskgraph.loader.single_dep:loader
 
 transforms:
     - taskgraph.transforms.name_sanity:transforms
     - taskgraph.transforms.repackage:transforms
-    - taskgraph.transforms.use_toolchains:transforms
     - taskgraph.transforms.job:transforms
     - taskgraph.transforms.task:transforms
 
 kind-dependencies:
     - repackage-signing
     - repackage-signing-l10n
     - fetch