Firefox 158 slow to exit

[libove]

There are many posts here about Firefox being "slow". I don't find that, most of the time, operations in recent Firefox are slow, however, EXITING Firefox in very recent versions (and particularly with v158 including v158.0.1) can be quite slow. (This is on Windows 11, 64-bit, 25H2, 26H2).

I routinely use Firefox only for a small number of fixed, long-running tabs - a Google Translate, a couple of other linguistic tools, and WhatsApp Web (which is almost certainly the instigator).

When I click to exit Firefox, I can sit staring at Task Manager as the Firefox processes gradually drop off until the program has fully existed, taking as much as a full minute+ (on a 4-core/8-thread 3.8GHz Xeon CPU with 32G RAM, all PCIe NVMe storage, not heavily loaded machine; other than that it is managed by Microsoft Intune and does have Microsoft's MsSense and MsMpEng security tasks operating).

[dftf]

@libove : try tapping ALT to show the old menubar, then on the "Profiles" menu, use "+ New Profile" to create a new one.  In that new profile, don't install any extensions, or change any default settings.

Close Firefox, and wait for all firefox.exe processes to clear.

Next time you start Firefox up, it should ask which profile to use: go into the new one.  Try some of the sites you usually would and see when closing Firefox if its processes are still hanging-around.

If they don't, it's likely an extension causing the issue.

Also type about:preferences#permissionsData in the URL bar, then press ENTER.
Then go into "Notifications" and see if you've allowed any page to send you alerts (e.g. news sites).
If so, it's common for firefox.exe processes to still run after exit, or such notifications wouldn't reach you.

[libove]

As for Notifications, I have those globally disabled in all of my web browsers. Annoying things, Notifications.

Why set up a new profile, if the goal is to test whether a particular site keeps background processes on exit? And, since Firefox though slow to exit does exit, why would we suspect that a site keeps a background process running - if that were the case, we would see Firefox NOT exit rather than take seconds to a minute+ to exit, right?

Further to "why setup a new profile", the sites and extensions that I use are the sites and extensions that I (need/want to) use, so getting rid of them wouldn't debug why it (only in somewhat recent times) causes Firefox to take a long time to exit.

Instead, how do we identify what is keeping Firefox busy between "Menu -> exit" and "Last Firefox .exe process exits"?

thank you,

[dftf]

Okay, so you have no site notifications active, so that can be ruled-out.

Faulty extensions (or a corrupt profile) can cause Firefox to hang when existing, hence why I suggested trying a new profile, then visiting the websites you usually use to see if that happens.  You can switch back to your current profile at any-time, so you won't lose anything.  There is also "Troubleshoot Mode" you could use instead (Menu -> Help and Report -> Troubleshoot Mode), which is like having a temporary new profile.  Try your usual sites in there; do firefox.exe processes all exit quickly after closing a Troubleshoot Mode window?

The only other things I can think of that might do this:

Anti-virus or anti-malware (or some other security software, especially if this is a corporate issued PC, not a personal one) might not be releasing the Firefox process immediately.  You could perhaps try the "Process Monitor" tool from Microsoft to inspect what is hooking into Firefox:
https://learn.microsoft.com/en-us/sysinternals/downloads/procmon

Or your Firefox could be failing to install an update in the background, as updates usually get applied whenever you fully-close the browser.  Maybe it's constantly trying to install the same update, but is failing?  Perhaps visit https://www.firefox.com/download/all/desktop-release/ , download a fresh installer, go to Start -> Settings -> Apps and then remove "Mozilla Maintenance Service", then "Mozilla Firefox", reboot, and install it fresh?  It'll link back into your previous profiles, so you won't lose anything.  But you could also do Menu -> Settings -> Accounts and Synchronisation -> Turn on backup (unless you're using it already) first, to be safe.

Perhaps also type about:crashes into the URL bar and press ENTER and see if anything is listed there; are there many recent crashes?  Or type reliability into the Start Menu, then click "View reliability history".  Is Firefox listed at the bottom when you click on any day?

[grundt]

What you're describing libove sounds like
2040781 - Firefox leaves itself in memory and prevents other programs from running correctly 
or maybe
2063567 - shutting down firefox browser sometimes leaves the process still running 

[libove]

Oh, about:Crashes - no crashes have been reported.

[libove]

It's not an unapplied update. I actively monitor software updates with a commercial MDM.

Report 2040781 suggests that Firefox never exits; in the cases I've seen, it does exit, it just takes far too long to do so.

Report 2063567 _might_ be related, but as that person expects Firefox to exit *instantly* (and, let's face it, with a dozen threads and using a total of some gigabytes of memory, we do need to let Firefox have a few seconds to exit, not to expect "instantly"), I'm not sure how realistic that report is in any case.

However, that points me to Firefox Profile and to about:memory, which when I have time I'll look at to see if they might provide some information useful to the concern.

That said, Firefox 159 was just released, and it explicitly addressed some memory performance issues, so for now I'm crossing my fingers and hoping that the problem will have gone away...