--- a/taskcluster/ci/desktop-test/tests.yml
+++ b/taskcluster/ci/desktop-test/tests.yml
@@ -48,30 +48,32 @@ external-media-tests:
             - mozharness/configs/remove_executables.py
 
 firefox-ui-functional-local:
     description: "Firefox-ui-tests functional run"
     suite: "firefox-ui/functional local"
     treeherder-symbol: tc-Fxfn-l(en-US)
     max-run-time: 5400
     tier: 1
+    docker-image: {"in-tree": "desktop1604-test"}
     mozharness:
         script: mozharness/scripts/firefox_ui_tests/functional.py
         config:
             - mozharness/configs/firefox_ui_tests/taskcluster.py
             - mozharness/configs/remove_executables.py
         extra-options:
             - "--tag local"
 
 firefox-ui-functional-remote:
     description: "Firefox-ui-tests functional run"
     suite: "firefox-ui/functional remote"
     treeherder-symbol: tc-Fxfn-r(en-US)
     max-run-time: 5400
     tier: 2
+    docker-image: {"in-tree": "desktop1604-test"}
     mozharness:
         script: mozharness/scripts/firefox_ui_tests/functional.py
         config:
             - mozharness/configs/firefox_ui_tests/taskcluster.py
             - mozharness/configs/remove_executables.py
         extra-options:
             - "--tag remote"