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Let's say, Firefox's instance is running with profile 1. Is it now possible, to start a new Firefox instance with profile 2?

Normally, when Firefox is already running, no new instance is created. Instead, just a new browser window is opened.

Note: By saying "profile", I'm referring to Firefox user profiles.

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try searching. it is the number one question regarding firefox in superuser.com –  barraponto Jan 25 '10 at 15:08

6 Answers 6

up vote 4 down vote accepted

Here's an article from Lifehacker dealing with this. It's not extremely complicated, I've used this a couple of times.

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Wow! Couldn't imagine that it's so simple and supported out-of-the-box ;) Thanks! –  linux_is_for_desktop Sep 15 '09 at 8:14

Using an unx environement, you can use a command like :

env MOZ_NO_REMOTE=1 firefox -P Profile2

Using a windows or Mac OS X env, I don't know how you can do it

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OSX is pretty much an unx environment, so it works there as well. –  Erika Sep 19 '13 at 14:15

Try MultiFirefox:

MultiFirefox is a small launcher utility that allows you to run multiple versions of Firefox side-by-side. It helps you set up multiple profiles (one or more for each version of Firefox), remembers your last launch preferences for easy launching, has auto-updating built in for when we make improvements, and is 100% open source, MIT licensed.

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Welcome to SU. Please provide more information then just a link. SU is a repository of answers and desciptive answers are encouraged. –  Diago Sep 15 '09 at 11:25
It is an external tool, which allows multiple instances of firefox to be started, also with different profiles and different sets of addons. –  brandstaetter Sep 15 '09 at 11:27
Thanks brandstaetter looks very interesting. –  Yar Sep 15 '09 at 11:33
Also, it is way more comfortable than using the built-in profile manager. Give it a try, a frined uses it all the time: He launches one instance for web developing with loads of add-ons, and one sleek with minimal add-ons for the usual web surfing, without the add-on bloat. –  brandstaetter Sep 15 '09 at 11:37
@brandstaetter: I edited your answer a bit to add more info about the app from the authors site. Hope you don't mind! Also, cool little app :) –  alex Sep 15 '09 at 12:04

You can do it from the command line:

firefox -no-remote -P profile_name
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First run 'firefox --profilemanager' to set up separate profiles. –  postfuturist Oct 30 '09 at 22:23
-P is a shorthand for that –  hasen Oct 31 '09 at 23:25
It isn't really: -P says 'load the named profile' it will only open ProfileManager it the profile you've named doesn't exist. –  robertc Jan 25 '10 at 14:11

I recommend:


Multifox is an extension that allows Firefox to connect to websites using different user names. Simultaneously!

For example, if you have multiple Gmail accounts, you can open them all at the same time. Each Firefox window, managed by Multifox, accesses an account without interfering each other

Each Multifox window is flagged with a number indicating the identity profile. Logins made in windows with different numbers are isolated.

Logins are preserved the same way they are in “regular” windows. Even if you close the window or quit Firefox.

The identity profile of each window is preserved when Firefox restores the session.

It can also easily switch between profiles:
enter image description here

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