Filed by: abutkovits [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer?job_id=359366163&repo=autoland
Full log: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/UtYvj8fMRqePDNeY8W5vfg/runs/0/artifacts/public/logs/live_backing.log

[task 2021-11-26T13:28:53.570Z] 13:28:53     INFO - TEST-START | toolkit/components/pictureinpicture/tests/browser_keyboardShortcutClosePIP.js
[task 2021-11-26T13:29:38.597Z] 13:29:38     INFO - TEST-INFO | started process screentopng
[task 2021-11-26T13:29:39.056Z] 13:29:39     INFO - TEST-INFO | screentopng: exit 0
[task 2021-11-26T13:29:39.057Z] 13:29:39     INFO - Buffered messages logged at 13:28:53
[task 2021-11-26T13:29:39.057Z] 13:29:39     INFO - Entering test bound test_pip_close_keyboard_shortcut
[task 2021-11-26T13:29:39.060Z] 13:29:39     INFO - Waiting for videos to be ready
[task 2021-11-26T13:29:39.061Z] 13:29:39     INFO - Waiting for 'canplaythrough' for 'no-controls'
[task 2021-11-26T13:29:39.062Z] 13:29:39     INFO - Buffered messages finished
[task 2021-11-26T13:29:39.063Z] 13:29:39     INFO - TEST-UNEXPECTED-FAIL | toolkit/components/pictureinpicture/tests/browser_keyboardShortcutClosePIP.js | Test timed out - 
[task 2021-11-26T13:29:39.063Z] 13:29:39     INFO - GECKO(18622) | MEMORY STAT | vsize 3398MB | residentFast 325MB | heapAllocated 195MB
[task 2021-11-26T13:29:39.064Z] 13:29:39     INFO - TEST-OK | toolkit/components/pictureinpicture/tests/browser_keyboardShortcutClosePIP.js | took 45028ms
[task 2021-11-26T13:29:39.064Z] 13:29:39     INFO - Not taking screenshot here: see the one that was previously logged
[task 2021-11-26T13:29:39.065Z] 13:29:39     INFO - TEST-UNEXPECTED-FAIL | toolkit/components/pictureinpicture/tests/browser_keyboardShortcutClosePIP.js | Found a tab after previous test timed out: http://example.com/browser/toolkit/components/pictureinpicture/tests/test-page.html - 
[task 2021-11-26T13:29:39.066Z] 13:29:39     INFO - checking window state

This is following Bug 1674666. I suspect that the test is failing pretty early due to ensureVideosReady() failing to resolve.
https://searchfox.org/mozilla-central/source/toolkit/components/pictureinpicture/tests/browser_keyboardShortcutClosePIP.js#17