--- a/taskcluster/docker/firefox-snap/snapcraft.yaml.in
+++ b/taskcluster/docker/firefox-snap/snapcraft.yaml.in
@@ -31,20 +31,16 @@ apps:
       - x11
 
 plugs:
   browser-sandbox:
     interface: browser-support
     allow-sandbox: true
 
 parts:
-  desktop-gtk3:
-    prime:
-      - -usr/share/mime
-
   firefox:
     plugin: dump
     source: source
     stage-packages:
       - libxt6
       - libdbus-glib-1-2
       - libasound2
       - libpulse0
@@ -67,19 +63,14 @@ parts:
       update-desktop-database -v $SNAPCRAFT_PART_INSTALL/usr/share/applications
     build-packages:
       - desktop-file-utils
     build-attributes: [no-system-libraries]
 
   shared-mime-info:
     after: [xdg-open]
     plugin: nil
-    source: .
-    build-packages:
+    stage-packages:
       - shared-mime-info
     build-attributes: [no-system-libraries]
     install: |
       set -eux
-      mkdir -p $SNAPCRAFT_PART_INSTALL/usr/share/mime/packages
-      install -m 644 mime-handler.xml $SNAPCRAFT_PART_INSTALL/usr/share/mime/packages
       update-mime-database $SNAPCRAFT_PART_INSTALL/usr/share/mime
-    stage:
-      - usr/share/mime