Firefox processes keep running at Quit

[Dominique_71]

I saw that sometime, especially when many tabs are open, firefox can be very slow when quitting. htop show me that it close its GUI and many processes relatively fast, but some processes keep running. I found 2 ways to close them: "killall -9 firefox" or shut down the internet connection. In both cases, the remaining processes are closing immediately.

How can I know why firefox keep these processes open and what they are doing?

Is it some firefox setting I can change that will block this?

Edit: or maybe part of the best solution is to run firefox into a docker container... but I which I can investigate that issue.
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