--- a/taskcluster/ci/test/test-platforms.yml
+++ b/taskcluster/ci/test/test-platforms.yml
@@ -21,39 +21,42 @@ linux32/debug:
         - linux32-tests
         - external-media-tests
 linux32/opt:
     build-platform: linux/opt
     test-sets:
         -  linux32-tests
         -  linux32-opt-tests
         - external-media-tests
+        - external-media-tests-slow
 
 linux64/debug:
     build-platform: linux64/debug
     test-sets:
         - common-tests
         - external-media-tests
         - web-platform-tests
 linux64/opt:
     build-platform: linux64/opt
     test-sets:
         - common-tests
         - external-media-tests
+        - external-media-tests-slow
         - web-platform-tests
         - opt-only-tests
         - desktop-screenshot-capture
         - talos
 
 # TODO: use 'pgo' and 'asan' labels here, instead of -pgo/opt
 linux64-pgo/opt:
     build-platform: linux64-pgo/opt
     test-sets:
         - common-tests
         - external-media-tests
+        - external-media-tests-slow
         - web-platform-tests
         - talos
 
 linux64-asan/opt:
     build-platform: linux64-asan/opt
     test-sets:
         - common-tests
 
@@ -98,16 +101,17 @@ windows7-32-vm/debug:
     test-sets:
         - windows-vm-tests
         - external-media-tests
 windows7-32-vm/opt:
     build-platform: win32/opt
     test-sets:
         - windows-vm-tests
         - external-media-tests
+        - external-media-tests-slow
 
 # win32 gpu
 #windows7-32/debug:
 #    build-platform: win32/debug
 #    test-sets:
 #        - windows-gpu-tests
 #windows7-32/opt:
 #    build-platform: win32/opt
@@ -120,16 +124,17 @@ windows10-64-vm/debug:
     test-sets:
         - windows-vm-tests
         - external-media-tests
 windows10-64-vm/opt:
     build-platform: win64/opt
     test-sets:
         - windows-vm-tests
         - external-media-tests
+        - external-media-tests-slow
 
 # win64 gpu
 #windows10-64/debug:
 #    build-platform: win64/debug
 #    test-sets:
 #        - windows-gpu-tests
 #windows10-64/opt:
 #    build-platform: win64/opt

--- a/taskcluster/ci/test/test-sets.yml
+++ b/taskcluster/ci/test/test-sets.yml
@@ -41,16 +41,19 @@ common-tests:
 web-platform-tests:
     - web-platform-tests
     - web-platform-tests-reftests
     - web-platform-tests-wdspec
 
 external-media-tests:
     - external-media-tests-base
     - external-media-tests-youtube
+
+external-media-tests-slow:
+    # twitch tests are too slow and stall under debug, give them their own special set
     - external-media-tests-twitch
 
 opt-only-tests:
     - mochitest-valgrind
 
 talos:
     - talos-chrome
     - talos-dromaeojs