Steps to reproduce:

1. User starts Firefox ("version 97.0.1") using profile "P1".
2. Mozilla pushes update to Firefox ("version 97.0.2") .
3. User starts another instance of Firefox using profile "P2".

Alternative timeline to consider:

• Update was published before step 1, but was only applied at step 3.

Actual results:

4. User observed that, in the second instance (profile "P2"), only the first tab loaded/rendered, however, most of the new tabs didn't load/render anything, and they were all from the same website. [Didn't check if this issue also applied to the first instance using profile "P1".]

• Refreshing such a tab had no effect.
• Closing such a tab and re-opening the same link had no effect; a new tab opens, but nothing loads/renders.

5. Help About in the second instance (profile "P2") showed a message saying something like, "Firefox is being updated by another process".

This has happened at least five times over a period of several months/updates.

Expected results:

New tabs should have opened/rendered normally after starting Firefox with a different profile.

Comments:

• Win32 x64
• All Firefox profiles are incognito.
• This has happened several times in the last several months, and may be related to an update being applied between the user starting the first instance--before any update is available, or applied--and the second instance using a different profile, after a new update has been published, and possibly applied.
• Resolved by closing all instances of Firefox, killing all pending Firefox processes, then starting Firefox using the different profiles again. Help About now shows "Firefox is up to date" in all profiles/instances.

The Bugbug bot thinks this bug should belong to the 'Toolkit::Startup and Profile System' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

The severity field is not set for this bug.
:mossop, could you have a look please?

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