User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.11 Safari/537.36 Steps to reproduce: I was browsing webpages by Firefox 37.0.0.5532 on Windows Server 2008 R2 SP3 64bit. Actual results: Suddenly it get unable to show new pages. After that, the Firefox process remains until Windows restarts even if the user closes all window. If the user tries to restart Firefox, it will only show error messages that it cannot open the user profile. Process Explorer shows firefox.exe have a remaining thread. The stack trace, which is attached, shows PR_Close is blocking in kernel mode. Expected results: Firefox should show new pages and the process should terminate.

This is the stack frame of the thread taken by Process Hacker.

See also: http://forums.mozillazine.org/viewtopic.php?f=38&t=2916383&start=15

Try https://developer.mozilla.org/en-US/docs/How_to_Report_a_Hung_Firefox to get a stack trace with symbols. See also bug 1125686 comment 7, you may be having the same issue.

I don't see this problem on recent versions. It seems to be fixed.

OK, thanks for the update!