Filed by: ctuns [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer?job_id=370991813&repo=autoland
Full log: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/MW5qVDB5T3uhigFPn9KxFA/runs/0/artifacts/public/logs/live_backing.log
Reftest URL: https://hg.mozilla.org/mozilla-central/raw-file/tip/layout/tools/reftest/reftest-analyzer.xhtml#logurl=https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/MW5qVDB5T3uhigFPn9KxFA/runs/0/artifacts/public/logs/live_backing.log&only_show_unexpected=1

[task 2022-03-14T16:47:03.674Z] 16:47:03     INFO - TEST-PASS | browser/components/customizableui/test/browser_remote_tabs_button.js | The sync remote tabs button was added to the Panel Menu - 
[task 2022-03-14T16:47:03.675Z] 16:47:03     INFO - Buffered messages finished
[task 2022-03-14T16:47:03.680Z] 16:47:03     INFO - TEST-UNEXPECTED-FAIL | browser/components/customizableui/test/browser_remote_tabs_button.js | Test timed out - 
[task 2022-03-14T16:47:03.681Z] 16:47:03     INFO - Not taking screenshot here: see the one that was previously logged
[task 2022-03-14T16:47:03.682Z] 16:47:03     INFO - TEST-UNEXPECTED-FAIL | browser/components/customizableui/test/browser_remote_tabs_button.js | Uncaught exception received from previously timed out test - ViewShown listener on #PanelUI-remotetabs not removed before the end of test
[task 2022-03-14T16:47:03.682Z] 16:47:03     INFO - Entering test bound asyncCleanup
[task 2022-03-14T16:47:03.682Z] 16:47:03     INFO - TEST-PASS | browser/components/customizableui/test/browser_remote_tabs_button.js | The panel UI is in default state again. - 
[task 2022-03-14T16:47:03.682Z] 16:47:03     INFO - Leaving test bound asyncCleanup
[task 2022-03-14T16:47:03.682Z] 16:47:03     INFO - GECKO(10858) | MEMORY STAT vsizeMaxContiguous not supported in this build configuration.
[task 2022-03-14T16:47:03.682Z] 16:47:03     INFO - GECKO(10858) | MEMORY STAT | vsize 3193MB | residentFast 461MB | heapAllocated 215MB
[task 2022-03-14T16:47:03.683Z] 16:47:03     INFO - TEST-OK | browser/components/customizableui/test/browser_remote_tabs_button.js | took 45163ms
[task 2022-03-14T16:47:03.683Z] 16:47:03     INFO - checking window state
[task 2022-03-14T16:47:03.683Z] 16:47:03     INFO - GECKO(10858) | Completed ShutdownLeaks collections in process 10858
[task 2022-03-14T16:47:03.683Z] 16:47:03     INFO - TEST-START | Shutdown

First appeared on backout of 1758476, https://treeherder.mozilla.org/jobs?repo=autoland&selectedTaskRun=PvFd_5raQaSe-dKiKcEtbA.0&resultStatus=testfailed%2Cbusted%2Cexception%2Cusercancel&revision=76c68029dfca33c918cdb9abb6c66d4876aafcda

:standard8, since you are the author of the regressor, bug 1758476, could you take a look?
For more information, please visit auto_nag documentation.

If the backout of bug 1758476 fixed this, then it isn't a regressor. It was presumably pre-existing, though I really don't see how any of the changes there would have fixed or broken this.

https://wiki.mozilla.org/Bug_Triage#Intermittent_Test_Failure_Cleanup
For more information, please visit auto_nag documentation.