--- a/netwerk/test/unit/test_http2-proxy.js
+++ b/netwerk/test/unit/test_http2-proxy.js
@@ -365,17 +365,17 @@ add_task(async function setup() {
     processId,
     `http2ProxyCode.startNewProxy()`
   );
   proxy_port = proxy.port;
   Assert.notEqual(proxy_port, null);
 
   Services.prefs.setStringPref(
     "services.settings.server",
-    `data:text/html,test`
+    `data:,#remote-settings-dummy/v1`
   );
 
   Services.prefs.setBoolPref("network.http.http2.enabled", true);
 
   // Even with network state isolation active, we don't end up using the
   // partitioned principal.
   Services.prefs.setBoolPref("privacy.partition.network_state", true);
 

--- a/netwerk/test/unit/test_http2_with_proxy.js
+++ b/netwerk/test/unit/test_http2_with_proxy.js
@@ -44,17 +44,17 @@ add_setup(async function setup() {
   );
 
   loadGroup = Cc["@mozilla.org/network/load-group;1"].createInstance(
     Ci.nsILoadGroup
   );
 
   Services.prefs.setStringPref(
     "services.settings.server",
-    `data:text/html,test`
+    `data:,#remote-settings-dummy/v1`
   );
 
   proxy = new NodeHTTP2ProxyServer();
   await proxy.start();
 });
 
 registerCleanupFunction(async () => {
   Services.prefs.clearUserPref("network.http.speculative-parallel-limit");

--- a/testing/marionette/client/marionette_driver/geckoinstance.py
+++ b/testing/marionette/client/marionette_driver/geckoinstance.py
@@ -139,17 +139,17 @@ class GeckoInstance(object):
         "privacy.trackingprotection.enabled": False,
         # Disable recommended automation prefs in CI
         "remote.prefs.recommended": False,
         # Don't do network connections for mitm priming
         "security.certerrors.mitm.priming.enabled": False,
         # Tests don't wait for the notification button security delay
         "security.notification_enable_delay": 0,
         # Ensure blocklist updates don't hit the network
-        "services.settings.server": "http://%(server)s/dummy/blocklist/",
+        "services.settings.server": "data:,#remote-settings-dummy/v1",
         # Disable password capture, so that tests that include forms aren"t
         # influenced by the presence of the persistent doorhanger notification
         "signon.rememberSignons": False,
         # Prevent starting into safe mode after application crashes
         "toolkit.startup.max_resumed_crashes": -1,
         # Disable most telemetry pings
         "toolkit.telemetry.server": "https://%(server)s/telemetry-dummy/",
         # Disable window occlusion on Windows, see Bug 1802473.

--- a/testing/profiles/common/user.js
+++ b/testing/profiles/common/user.js
@@ -54,17 +54,17 @@ user_pref("general.useragent.updates.ena
 user_pref("hangmonitor.timeout", 0); // no hang monitor
 user_pref("media.gmp-manager.updateEnabled", false);
 // Don't do network connections for mitm priming
 user_pref("security.certerrors.mitm.priming.enabled", false);
 // Enable some dangerous features for test code. :-(
 user_pref("security.turn_off_all_security_so_that_viruses_can_take_over_this_computer", true);
 user_pref("xpinstall.signatures.required", false);
 // Prevent Remote Settings to issue non local connections.
-user_pref("services.settings.server", "http://localhost/remote-settings-dummy/v1");
+user_pref("services.settings.server", "data:,#remote-settings-dummy/v1");
 // Ensure autoplay is enabled for all platforms.
 user_pref("media.autoplay.default", 0); // 0=Allowed, 1=Blocked, 2=Prompt
 user_pref("media.autoplay.blocking_policy", 0);
 user_pref("media.autoplay.ask-permission", false);
 user_pref("media.autoplay.block-webaudio", false);
 user_pref("media.allowed-to-play.enabled", true);
 // Ensure media can always play without delay
 user_pref("media.block-autoplay-until-in-foreground", false);

--- a/testing/profiles/unittest-required/user.js
+++ b/testing/profiles/unittest-required/user.js
@@ -194,17 +194,17 @@ user_pref("privacy.trackingprotection.in
 // Disable all recommended Remote Protocol preferences for Gecko tests.
 // The prefs recommended by Remote Protocol are typically geared towards
 // consumer automation; not vendor testing.
 user_pref("remote.prefs.recommended", false);
 user_pref("security.default_personal_cert", "Select Automatically"); // Need to client auth test be w/o any dialogs
 // Existing tests don't wait for the notification button security delay
 user_pref("security.notification_enable_delay", 0);
 // Ensure blocklist updates don't hit the network
-user_pref("services.settings.server", "http://{server}/dummy-kinto/v1");
+user_pref("services.settings.server", "data:,#remote-settings-dummy/v1");
 user_pref("shell.checkDefaultClient", false);
 // Disable password capture, so that mochitests that include forms aren't
 // influenced by the presence of the persistent doorhanger notification.
 user_pref("signon.rememberSignons", false);
 user_pref("startup.homepage_welcome_url", "about:blank");
 user_pref("startup.homepage_welcome_url.additional", "");
 user_pref("test.mousescroll", true);
 // Don't send 'bhr' ping during tests, otherwise the testing framework might

--- a/testing/profiles/xpcshell/user.js
+++ b/testing/profiles/xpcshell/user.js
@@ -15,17 +15,17 @@ user_pref("extensions.webextensions.warn
 user_pref("geo.provider.testing", true);
 user_pref("browser.region.network.url", "");
 user_pref("geo.provider.network.compare.url", "");
 user_pref("media.gmp-manager.updateEnabled", false);
 user_pref("media.gmp-manager.url.override", "http://%(server)s/dummy-gmp-manager.xml");
 user_pref("toolkit.telemetry.server", "https://%(server)s/telemetry-dummy");
 user_pref("telemetry.fog.test.localhost_port", -1);
 // Prevent Remote Settings to issue non local connections.
-user_pref("services.settings.server", "http://localhost/remote-settings-dummy/v1");
+user_pref("services.settings.server", "data:,#remote-settings-dummy/v1");
 // Prevent intermediate preloads to be downloaded on Remote Settings polling.
 user_pref("security.remote_settings.intermediates.enabled", false);
 // The process priority manager only shifts priorities when it has at least
 // one active tab. xpcshell tabs don't have any active tabs, which would mean
 // all processes would run at low priority, which is not desirable, so we
 // disable the process priority manager entirely here.
 user_pref("dom.ipc.processPriorityManager.enabled", false);
 // Avoid idle-daily notifications, to avoid expensive operations that may

--- a/toolkit/components/extensions/test/xpcshell/webidl-api/xpcshell.ini
+++ b/toolkit/components/extensions/test/xpcshell/webidl-api/xpcshell.ini
@@ -11,17 +11,17 @@ prefs =
   # Enable ExtensionMockAPI WebIDL bindings used for unit tests
   # related to the API request forwarding and not tied to a particular
   # extension API.
   extensions.webidl-api.expose_mock_interface=true
   # Make sure that loading the default settings for url-classifier-skip-urls
   # doesn't interfere with running our tests while IDB operations are in
   # flight by overriding the remote settings server URL to
   # ensure that the IDB database isn't created in the first place.
-  services.settings.server=http://localhost:7777/remote-settings-dummy/v1
+  services.settings.server=data:,#remote-settings-dummy/v1
 
 # NOTE: these tests seems to be timing out because it takes too much time to
 # run all tests and then fully exiting the test.
 skip-if = os == "android" && verify
 
 [test_ext_webidl_api.js]
 [test_ext_webidl_api_event_callback.js]
 skip-if =

--- a/toolkit/components/extensions/test/xpcshell/xpcshell-e10s.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell-e10s.ini
@@ -9,17 +9,17 @@ support-files =
   xpcshell-content.ini
 tags = webextensions webextensions-e10s
 
 # Make sure that loading the default settings for url-classifier-skip-urls
 # doesn't interfere with running our tests while IDB operations are in
 # flight by overriding the remote settings server URL to
 # ensure that the IDB database isn't created in the first place.
 prefs =
-  services.settings.server=http://localhost:7777/remote-settings-dummy/v1
+  services.settings.server=data:,#remote-settings-dummy/v1
 
 [include:xpcshell-common-e10s.ini]
 skip-if =
   socketprocess_networking # Bug 1759035
 [include:xpcshell-content.ini]
 skip-if =
   socketprocess_networking && fission # Bug 1759035
 

--- a/toolkit/components/extensions/test/xpcshell/xpcshell-legacy-ep.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell-legacy-ep.ini
@@ -5,17 +5,17 @@ firefox-appdir = browser
 skip-if = appname == "thunderbird" || os == "android"
 dupe-manifest =
 
 # Make sure that loading the default settings for url-classifier-skip-urls
 # doesn't interfere with running our tests while IDB operations are in
 # flight by overriding the remote settings server URL to
 # ensure that the IDB database isn't created in the first place.
 prefs =
-  services.settings.server=http://localhost:7777/remote-settings-dummy/v1
+  services.settings.server=data:,#remote-settings-dummy/v1
 
 # Bug 1646182: Test the legacy ExtensionPermission backend until we fully
 # migrate to rkv
 [test_ext_permissions.js]
 [test_ext_permissions_api.js]
 [test_ext_permissions_migrate.js]
 [test_ext_permissions_uninstall.js]
 [test_ext_proxy_config.js]

--- a/toolkit/components/extensions/test/xpcshell/xpcshell-remote.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell-remote.ini
@@ -14,17 +14,17 @@ support-files =
   xpcshell-content.ini
 tags = webextensions remote-webextensions
 
 # Make sure that loading the default settings for url-classifier-skip-urls
 # doesn't interfere with running our tests while IDB operations are in
 # flight by overriding the remote settings server URL to
 # ensure that the IDB database isn't created in the first place.
 prefs =
-  services.settings.server=http://localhost:7777/remote-settings-dummy/v1
+  services.settings.server=data:,#remote-settings-dummy/v1
 
 [include:xpcshell-common.ini]
 skip-if =
   os == "linux" && socketprocess_networking # Bug 1759035
 [include:xpcshell-common-e10s.ini]
 skip-if =
   os == "linux" && socketprocess_networking # Bug 1759035
 [include:xpcshell-content.ini]

--- a/toolkit/components/extensions/test/xpcshell/xpcshell.ini
+++ b/toolkit/components/extensions/test/xpcshell/xpcshell.ini
@@ -8,17 +8,17 @@ support-files =
   xpcshell-content.ini
 tags = webextensions in-process-webextensions condprof
 
 # Make sure that loading the default settings for url-classifier-skip-urls
 # doesn't interfere with running our tests while IDB operations are in
 # flight by overriding the remote settings server URL to
 # ensure that the IDB database isn't created in the first place.
 prefs =
-  services.settings.server=http://localhost:7777/remote-settings-dummy/v1
+  services.settings.server=data:,#remote-settings-dummy/v1
 
 # This file contains tests which are not affected by multi-process
 # configuration, or do not support out-of-process content or extensions
 # for one reason or another.
 #
 # Tests which are affected by remote content or remote extensions should
 # go in one of:
 #

--- a/toolkit/mozapps/extensions/internal/AddonTestUtils.jsm
+++ b/toolkit/mozapps/extensions/internal/AddonTestUtils.jsm
@@ -283,17 +283,17 @@ var AddonTestUtils = {
       "http://127.0.0.1/updateURL"
     );
     Services.prefs.setCharPref(
       "extensions.update.background.url",
       "http://127.0.0.1/updateBackgroundURL"
     );
     Services.prefs.setCharPref(
       "services.settings.server",
-      "http://localhost/dummy-kinto/v1"
+      "data:,#remote-settings-dummy/v1"
     );
 
     // By default ignore bundled add-ons
     Services.prefs.setBoolPref("extensions.installDistroAddons", false);
 
     // Ensure signature checks are enabled by default
     Services.prefs.setBoolPref("xpinstall.signatures.required", true);
 

--- a/toolkit/mozapps/extensions/test/xpcshell/rs-blocklist/test_blocklist_mlbf_fetch.js
+++ b/toolkit/mozapps/extensions/test/xpcshell/rs-blocklist/test_blocklist_mlbf_fetch.js
@@ -28,17 +28,17 @@ add_task(async function fetch_invalid_ml
   // the application. This test intentionally hides the actual path to get
   // deterministic results. To check whether the dump is correctly registered,
   // run test_blocklist_mlbf_dump.js
 
   // Forget about the packaged attachment.
   Downloader._RESOURCE_BASE_URL = "invalid://bogus";
   // NetworkError is expected here. The JSON.parse error could be triggered via
   // _baseAttachmentsURL < downloadAsBytes < download < download < _fetchMLBF if
-  // the request to  services.settings.server (http://localhost/dummy-kinto/v1)
+  // the request to  services.settings.server ("data:,#remote-settings-dummy/v1")
   // is fulfilled (but with invalid JSON). That request is not expected to be
   // fulfilled in the first place, but that is not a concern of this test.
   // This test passes if _fetchMLBF() rejects when given an invalid record.
   await Assert.rejects(
     ExtensionBlocklistMLBF._fetchMLBF(invalidRecord),
     /NetworkError|SyntaxError: JSON\.parse/,
     "record not found when there is no packaged MLBF"
   );