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On Windows If I run Firefox as user jack, and then try to start another instance of firefox I will be unable to, as one is already running.

If I choose to run firefox as administrator, then I can have two instances of firefox, separate from each other side by side, because they are under different user accounts.

This does not seem to be true on Linux.

As user jack if I start firefox, like on windows I am unable to start a new instance. If I open a terminal and change to root, set XAUTHORITY to jacks .Xauthority and try to start firefox as root....I get the error that firefox is already running.

Why is this? Please don't spare any technical details in your answers....thankyou.

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up vote 9 down vote accepted

Pass the --no-remote parameter to firefox on startup and it won't re-use the existing process.

This is a known issue with firefox on most unix platforms. What seems to happen is firefox queries the X server, sees that another firefox is running (it doesn't even have to be the same version) and sends it a signal to open a new page, rather than actually starting.

It even happens if the second firefox is started on a second machine over SSH with X forwarding enabled. It's a pet peeve of mine which still hasn't been fixed.

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Afaik, --no-remote can only be used along with -P parameter, so you cannot launch the same profile in different instances. Source: "no-remote - Enables running multiple instances of the application with different profiles; [1] used with -P" – Om Nom Nom May 4 '10 at 6:57
@om nom: Sounds reasonable, given that they still use that broken profile concept from the Dark Ages of Netscape on Windows 9x. – Joey May 4 '10 at 8:33
Interesting, thankyou. So this is a firefox specific bug, rather than any difference in the process model between Windows and Linux? – Jack May 4 '10 at 8:48
@OmNomNom: Only a problem if using the same user account. The OP is trying to use one instance as jack and another as root, each would use it's default profile from the corresponding home directory. And in my case, the profile is on another machine entirely. – developmentalinsanity May 4 '10 at 18:14
@Jack It's to do with how firefox does things. Has nothing to do with the process model. – developmentalinsanity May 5 '10 at 18:57

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