I understand that Firefox has to be closed to run CCleaner. Normally this is not a problem.
Today (October 09, 2019) Firefox unexpectedly closed while I was checking my Yahoo mail. I re-opened it and I finished, then closed Firefox. When I went to remove some cookies with CCleaner, I was informed that Firefox was still running, when it had been Closed and there was NO indication it was still running with (Windows 10) task manager. I opened Firefox (currently 69.0.2) then closed it twice before trying to remove some cookies with CCleaner. When I went to delete those cookies, I was informed that Firefox was still running. CCleaner opened a window that offered to terminate Firefox. I clicked the option to close Firefox. A few seconds later, I was told that Firefox was not closing and was offered an option to force it closed. I clicked that option and only then was I able to delete those cookies I wanted gone.
What does CCleaner use to determine that Firefox is NOT running? Does Firefox closing unexpectedly freeze this, whatever, to indicate that it did not close? Whose problem this is I don't know, but I have also informed Mozilla that there is a conflict with CCleaner when Firefox closes unexpectedly.
Problem solved, until the next time Firefox closes unexpectedly. I use Firefox almost exclusively.
One thing I've noticed over the last decade plus of using Firefox is it needs to be given ample time to fully close/exit, and sometimes it may take longer than usual or expected in some instances before attempting to clean it with CCleaner, etc. This holds true even on a modern computer with an SSD and a quick CPU.
I have NOT had a problem with Firefox taking an excessive time to close under NORMAL use. I have run CCleaner almost immediately after closing Firefox and never had to wait for the past several years. Firefox "closing unexpectedly" is NOT normal use!
I believe that you have already stated the cause of the problem - Firefox crashed in an unexpected manner, and left some component running.
(Sounds like the crash was caused by Yahoo mail, or maybe the contents of one particular email message?)
CCleaner eventually recognised that there was something unusual happening and, after asking your permission, forced the rouge process to close.
Modern Firefox starts multiple processes, you can see these in Task Manager.
Just what was left running after the Firefox crash I suspect will never be know now.
As for your other question, I would say that if CCleaner tries to delete something Firefox but Windows says 'you can't delete that because it's still in use' then it's a good assumption that some part of Firefox is still running and using it.
Exactly. As to exactly caused the crash, I will probably never know either (unless Mozilla can tell me from their crash reports).
Checking task manager doesn't help as much as it used to. A recent change, in windows 10, seems to place the "most used" program/ component at the top of the list and that listing order changes about every second, making it almost impossible to read!
Unless someone has found the cause and verified it, any other replies are useless.
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Nergal, I mostly use CCleaner to delete cookies and the browser cache. I DON'T mess with the registry, and that is NOT what I wrote.
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Your comments are not relevant.
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Um, I didn't say anything about registry, I said firefox sometimes leaves behind a plugincontainer or other process in task manager and that this is often caused a firefox addon.
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Checking task manager doesn't help as much as it used to. A recent change, in windows 10, seems to place the "most used" program/ component at the top of the list and that listing order changes about every second, making it almost impossible to read!
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Simply click on 'Name' (instead of CPU) in the task manager and the processes will be pinned in place by process type and name rather than jumping about to show the most used.
Note that FireFox will show processes in both 'Apps' and 'Background Processes' types.