There is a problem with intermittent failures in GitHub CI for the Puppeteer team as filed at:
https://github.com/puppeteer/puppeteer/issues/14194

A potential factor here seems to be the Backup Service:
https://firefox-source-docs.mozilla.org/browser/components/backup/docs/index.html

This service is not needed for usual testing and could potentially interfere with restoring backup'ed profiles on a users system.

We should disable this service by default for the Remote Agent by setting browser.backup.enabled to false in our recommended preferences.

This service is not necessary for web automation and testing.
As such it can be disabled by default for WebDriver protocols.

Maybe the hang that we can see might be related to our usage of browser-idle-startup-tasks-finished. Given that this task is getting initialized during that step something might cause it to break and the notification never to be fired. As discussed on bug 1982776 we should most likely move to using the browser-delayed-startup-finished notification instead. I'll file a bug for it soon.

Nevertheless the patch still stands and we should disable the service by default. CC mconley.

Even if an idle task throws an exception, I don't believe that should cause browser-idle-startup-tasks-finished to never fire. The subsequent idle tasks would run after the exception is thrown by the earlier one. Then, eventually, the notification is fired here: https://searchfox.org/firefox-main/rev/9ffc661a59959bcfdd1ac91119739ac76b778ee7/browser/base/content/browser-init.js#972-975

(In reply to Mike Conley (:mconley) (:⚙️) (PTO - Sept 15 - 19) from comment #3)

Even if an idle task throws an exception, I don't believe that should cause browser-idle-startup-tasks-finished to never fire. The subsequent idle tasks would run after the exception is thrown by the earlier one. Then, eventually, the notification is fired here: https://searchfox.org/firefox-main/rev/9ffc661a59959bcfdd1ac91119739ac76b778ee7/browser/base/content/browser-init.js#972-975

Thanks. Lets further discuss it over on bug 1988261.

This change is going to help at least Puppeteer to reduce their intermittent startup issue with Firefox even though not completely. I'm suggesting P2 given that it's not clear what the impact for other tools is, which as well use GitHub actions and run their tests with WebDriver in headful mode.

https://hg.mozilla.org/mozilla-central/rev/3a4e84975e95