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I see there are 20 tabs on my Firefox browser, but 31 Firefox processes in the Firefox process group in the Task Manager. I think one Firefox process corresponds to one tab, so why are there so many Firefox processes? How can I find the correspondence between a tab and a Firefox process?

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    An extension will use a process, and firefox itself will also use one. Maybe there's a database too that uses a process.
    – LPChip
    Commented May 30 at 8:56
  • it the past it was 4 tabs per process
    – phuclv
    Commented May 31 at 2:24

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I think one Firefox process corresponds to one tab, so why are there so many Firefox processes? How can I find the correspondence between a tab and a Firefox process?

Open about:processes in the address bar to see that information. Each process will be listed with the tabs it handles, and with the "(Process ID)" in parentheses that you can match against Task Manager's "Details" tab (or against ProcExp or SysInformer).

  • The main Firefox process (which handles the GUI, various things such as sync)
  • Approximately one "tab" process per tab (some tabs can share a process)
  • One process handling network communications
  • One process (or more) for extensions
  • One "Data decoder" process (which I think handles video decoding specifically)
  • A few "Utility" processes (for anything else that warrants isolation)
  • A few spare "preallocated" processes (to speed up opening of new tabs, as creating a new process is relatively slow, especially in Windows)
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    Re "Open about:processes": In what context? Inside Task Manager? In Firefox? Somewhere in Windows? Commented May 30 at 22:23
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    @PeterMortensen The about:keyword format is used in the firefox address bar to access various internal information/etc pages. about:config is probably the most commonly used one, giving access to a large number of low level settings in the browser. Commented May 31 at 0:28
  • @DanIsFiddlingByFirelight Surely the most used would be about:blank (or now about:newtab)? :) Also about:about shows a list of available pages.
    – Bob
    Commented Jun 3 at 2:25
  • @Bob Might be something I customized away (my browsers lost the right to put anything on the empty tab screen the day they got greedy and tried selling my eyeballs to chumbox grifters), but when I open a new tab (including by the about:whatevers you mentioned I get an address bar the suggestion text "Search with Google or enter address" with whitespace below. Not about:whatever. Even if one of those is the default shown, I wouldn't count it loading from Ctrl-T, etc as being used in any meaningful way. Commented Jun 3 at 2:42
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    @quill: That sounds like a feature that would only be enabled by default in test versions – 126 already has browser.tabs.tooltipsShowPidAndActiveness, but it's off by default since it would just be clutter for most users. Commented Jun 15 at 22:28

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