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Reproducible Hang on Quit


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Dear all,

I believe I have found a sadly reproducible hang using either the latest version of Firefox or Firefox Developer Edition.

Whenever the Malwarebytes extension is installed and Firefox is set up to clear its caches, cookies, and all site data on quit, the quitting process hangs. All that is required is to install the Malwarebytes extension and load its preferences before quitting Firefox. Simply installing the extension without having a look at the settings page does not seem to trigger the issue as reliably for me.

From this point onwards, any time Firefox is quit, it will hang, presumably while attempting to clean the contents of the user’s profile and something owned by Malwarebytes. Note that I was able to reproduce it on clean installs of both Firefox and Firefox Developer Edition with no other configuration changes and no other extensions, plug-ins, or themes installed.

Is anyone else seeing this?

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I'm not seeing this, but there may be a difference in our setups that may help the devs to track it down.

I'm not using the Firefox setting to clear cookies, I use the 'Forget Me Not' add-on to handle cookies.

I'm also not clearing 'Site Preferences'. (I recall there was an earlier issue with 'Site preferences' and the MB extension when CCleaner was incorretly clearing them).


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Thank you, nukecad. for chiming in! ?

I find it interesting that your results vary, as I can reproduce this pretty consistently… I did delete the Site Preferences in my testing, which may explain the discrepancy. I haven’t narrowed down my analysis to the one checkbox that might trigger the hang — only to the general “clear all” operation — and I am afraid I cannot afford to mess up my Firefox install yet again just now. There may also be a Mac vs. Windows issue at play, although Firefox is pretty consistent by design. ?

I do not think that external apps like CCleaner could cause a hang in this case, as they should only kick in after Firefox has quit, and not while it hangs trying to do so. Of course, such and app may corrupt things and prevent the extension from restarting properly, but I do not think it could interfere with the shutdown process per se. In any case, I am not using CCleaner, or anything similar, on this machine. ?

What do you think? ?

Edited by FJK
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I wasn't suggesting it was CCleaner this time, just pointing out that there was another, different, issue in the past with Firefox Site Preferences. (In particular with the database file 'permissions.sqlite ').

Just out of interest how are you closing Firefox, using the closebox 'X' or 'Exiting' from the 'File' menu or the 'Hamburger' menu?
Neither one has any different affect on mine, but you never know.


There may also be a Mac vs. Windows issue at play

Is yours a Mac? Mine is Windows 10. It may be relevant.

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Mine is indeed a Mac, and I am afraid I have no Windows 10 machine with which to test just at present…

As far as I know, there is only one way to quit Firefox on the Mac, and that is using File → Quit or ⌘-Q — or any other shortcut that results in the same command being sent. In that light, I cannot say that I have tried various ways of quitting Firefox beyond the official and obvious.

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  • 6 months later...

The same holds still in version 1.0.38

Two firefox-processes remain in memory (running with low CPU-usage). One has got simply "<path>\firefox.exe" as command line the other has got the very long

"C:\Program Files\Mozilla Firefox\firefox.exe" -contentproc --channel="11740.0.1299937968\2135590280" -parentBuildID 20190211233335 -greomni "C:\Program Files\Mozilla Firefox\omni.ja" -appomni "C:\Program Files\Mozilla Firefox\browser\omni.ja" -appdir "C:\Program Files\Mozilla Firefox\browser" - "C:\Users\petsi\AppData\LocalLow\Mozilla\Temp-{025607c3-1059-46dd-8b70-4c340ed01a4a}" 11740 "\\.\pipe\gecko-crash-server-pipe.11740" 1740 gpu

I disabled every extension except malwarebytes. Plugins are H264, widevine, and flash. Sytem is Win 10 Home 1809 (17763.316).


Your extension works fine during the session, but it keeps firefox busy when I want to exit the browser.

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