How to Run Firefox 4 and Firefox 3 At the Same Time?

Originally posted 2011-03-23 08:00:00.

I haven’t had the need to do this yet but thanks to @StephenCronin asking this question.

With Firefox 4 out yesterday, there are many extension developers who haven’t updated their add-ons yet. Or you may want to test your website on Firefox 3 while using Firefox 4 simultaneously.

Whatever the reason maybe, here is how you can run Firefox 4 and Firefox 3 at the same time.

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Only requirement to do this you have to use 2 different profiles. You don’t want to mess with a stable  profile anyways.

  1. Launch Firefox 4 from the Run command with the flags ‘-profilemanager –no-remote’ (without the quotes)
    Windows: “C:\Program Files\Mozilal Firefox4\firefox.exe” -profilemanager -no-remote
    Mac/
    Linux: //firefox4/firefox -profilemanager -no-remote
  2. Select your Firefox 4 profile
  3. Launch Firefox 3 from the Run command with the flags ‘-profilemanager –no-remote’ (without the quotes)
    Windows: “C:\Program Files\Mozilal Firefox3\firefox.exe” -profilemanager -no-remote
    Mac/
    Linux: /firefox3/firefox -profilemanager -no-remote
  4. Create a Firefox 3 profile if you don’t have one already and select it

This assumes you want to keep your current profile on Firefox 4. Just reverse it if you want it the other way.

This should let you run Firefox 4 and Firefox 3 simultaneously. You can also create shortcuts with these flags in place to launch them easily.

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    Interesting. With this tutorial, i can now use plugins from Firefox 3 as there are a lot of plugins that are not yet compatible with Firefox 4.

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    that is an amazing post! i really like it!

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    This is a great post – thanks – I’d like to get my hands on some of this stuff!

  • Rick Herns

    Those who want to get the best of both worlds can try and run Firefox 3 build, along with the Firefox 4 beta version simultaneously. If you try and run both the versions simultaneously it wont work because by default both of the versions will try and run on the same profile and resulting into the working of only one of the versions. But you can do a small modification to the profiles, you will be able to use both of the versions simultaneously.

  • Anonymous

    I see no use in running both at the same time  http://www.watdahell.com/

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    I learnt how to run firefox earlier i used to mozila but now i’ll use firefox