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I'm running a Firefox shortcut with the flags

-P default -no-remote

to launch Firefox 3.6 under the "default" profile. I do this because I'm running Firefox 4 under a "beta" profile, and with different profiles, I can run both Firefox 3.6 and 4 simultaneously. If I don't have different profiles, opening one Firefox opens another instance of the current running Firefox (if I have 4 open, and I try to launch 3.6, it will open another window for 4).

Before I added the profile flag, I could open a million Firefox 3.6 windows under the same profile. Now I can only open one window, and subsequent windows say "Firefox is already running, but not responding."

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up vote 2 down vote accepted

This is because Firefox uses some sort of locking mechanism so that only one Firefox process can access each profile, and I think that's to avoid corruption in the sqlite databases (places, bookmarks, history, etc).

If you start Firefox with -no-remote, it claims exclusive access to the profile ("default" in your case) and no other Firefox process can use it, even if the second instance is invoked without the -no-remote.

You can of course use Ctrl+N or File > New Window to create a new window from within Firefox.

The proper way around this is to run Firefox 4 with -no-remote, and invoke your Fx3.6 instances without that flag.

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Oh, you're right. I thought -no-remote was necessary to open different profiles under different instances of Firefox. – Corey Dec 7 '10 at 14:39

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