Filed by: ncsoregi [at] mozilla.com
Parsed log: https://treeherder.mozilla.org/logviewer?job_id=367371171&repo=mozilla-beta
Full log: https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/Zoy90L7KQPeMo8QnuBa1ig/runs/0/artifacts/public/logs/live_backing.log

[task 2022-02-10T11:40:43.748Z] 11:40:43     INFO - TEST-PASS | browser/components/tests/browser/browser_browserGlue_upgradeDialog.js | Incorrectly handling clicks would have triggered exception - true == true - 
[task 2022-02-10T11:40:43.749Z] 11:40:43     INFO - Buffered messages finished
[task 2022-02-10T11:40:43.750Z] 11:40:43     INFO - TEST-UNEXPECTED-FAIL | browser/components/tests/browser/browser_browserGlue_upgradeDialog.js | A promise chain failed to handle a rejection: null has no properties - stack: enableTheme@chrome://browser/content/upgradeDialog.js:93:23
[task 2022-02-10T11:40:43.750Z] 11:40:43     INFO - Rejection date: Thu Feb 10 2022 11:40:43 GMT+0000 (Coordinated Universal Time) - false == true - JS frame :: resource://testing-common/PromiseTestUtils.jsm :: assertNoUncaughtRejections :: line 271
[task 2022-02-10T11:40:43.750Z] 11:40:43     INFO - Stack trace:
[task 2022-02-10T11:40:43.750Z] 11:40:43     INFO - resource://testing-common/PromiseTestUtils.jsm:assertNoUncaughtRejections:271
[task 2022-02-10T11:40:43.750Z] 11:40:43     INFO - chrome://mochikit/content/browser-test.js:handleTask:1017
[task 2022-02-10T11:40:43.752Z] 11:40:43     INFO - Leaving test bound double_click
[task 2022-02-10T11:40:43.753Z] 11:40:43     INFO - Entering test bound theme_change
[task 2022-02-10T11:40:43.754Z] 11:40:43     INFO - Console message: [JavaScript Error: "TypeError: null has no properties" {file: "chrome://browser/content/upgradeDialog.js" line: 93}]
[task 2022-02-10T11:40:43.757Z] 11:40:43     INFO - Not taking screenshot here: see the one that was previously logged
[task 2022-02-10T11:40:43.758Z] 11:40:43     INFO - TEST-UNEXPECTED-FAIL | browser/components/tests/browser/browser_browserGlue_upgradeDialog.js | Uncaught exception in test - Theme is active - threw exception: TypeError: theme is null
[task 2022-02-10T11:40:43.759Z] 11:40:43     INFO - Not taking screenshot here: see the one that was previously logged

Fixed in bug 1754126
https://hg.mozilla.org/mozilla-central/rev/113b63526eb2
https://hg.mozilla.org/releases/mozilla-beta/rev/2ab8bfb06513