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Firefox can run in different profiles, that can be setup using different plugins, for different purposes such as basic web browsing, web development, trading on ebay etc...

Is it possible to run more than one of these at a time, or does Firefox always run as a singleton?

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Does it matter if each profile starts in different firefox process? also Windows or Linux? – Nima Jun 22 '12 at 13:49
Doesn't matter, Windows and Linux. – leeand00 Jun 22 '12 at 14:45
@Nima Is it possible to start different profiles in the same process but another window? – dash17291 Dec 1 '13 at 13:59
@dash17291 Sorry I don't know. – Nima Dec 2 '13 at 22:03
up vote 6 down vote accepted

You can start multiple instances of Firefox with different profiles using the -no-remote argument:

firefox -P <profile_name> -no-remote

However this solution as some drawbacks.

The -no-remote switch specificaly state that:

  • a new instance of Firefox should be started (instead of just open another window in a running instance)
  • the new instance should not accept remote commands

This implies that all Operative System integration is disabled (since this integration it's implemented using remote commands), and so, things like opening hyperlinks from other applications don't work.

To get around this issue you can open a Firefox instance without the -no-remote switch, and then open multiple other instances with -no-remote. The first instance will work as you are used to, and will open all hyperlinks from external applications. Have in mind that you cannot open two instances with the same profile.

One more point: allways use your default profile to run without -no-remote. This way you avoid to allways have to open a Firefox instance without the no-remote when you already have -no-remote instances running.

More information about -no-remote can be found here, including some discussions about this problem.

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Something to be aware of here. -no-remote prevents links from being opened by other programs in that session - so you'll want whichever one you wish to be able to open links from other programs in to be started without the -no-remote option - if all of them have it, you'll end up with another firefox being launched when you try to open links from programs. – Stephanie Jun 22 '12 at 22:01
Thank you for remind me of this. Please check my edit. – criziot Jun 23 '12 at 2:10

To have several Mozilla Firefox windows with different profiles open at the same time, using the newer flag -new-instance instead of -no-remote is friendlier to open web links from external programs such as Thunderbird, etc.

For example, in the properties of a desktop icon for each profile:

firefox -P <profile_name> -new-instance

See: Bug 716110 - split -new-instance flag out of existing -no-remote flag

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The "several Mozilla Firefox windows" are actually different instances each (as included in the name of the option). – dash17291 Dec 1 '13 at 14:09

I would just run them as different users, with different user specific settings/addons enabled.

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Start with Firefox version 13, the --new-instance switch is added. It is better to do it this way, with the help of a bash script:

firefox -P <profile_name> -remote "ping()" || firefox --new-instance -P <profile_name> <url> && firefox -P <profile_name> -remote "openurl(<url>,new-window)"

Changing from new-window to new-tab will cause the URL open in a new tab in profile instead.

Break it down:

firefox -P <profile_name> -remote "ping()"

does the running instance check.

|| firefox --new-instance -P <profile_name> <url>

double pipe || means if the check fails, it will start a new instance with given profile.

&& firefox -P <profile_name> -remote "openurl(<url>,new-window)"

and of course, && means, if the check succeeds, it will re-use the existing instance to open the URL in a new window.

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If you have Firefox Portable, it can be run separately from the non-portable Firefox installation in your computer. And although I haven't tried this (can someone confirm?), this possibly might also work with other Firefox Portable installations too.

Just set this is FirefoxPortable.ini (same directory as FirefoxPortable.exe)`


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