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I have Firefox 3.6 installed and have just seen that Firefox 4 Beta is available. Is it possible for me to install Firefox 4 Beta alongside my current Installation of Firefox?

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I no longer use Firefox, but when I did, their betas were pretty robust and I never bothered keeping an old install and never got burnt. Of course if you are developing against multiple revisions, ignore this. –  msw Jul 7 '10 at 16:45
    
@msw - I've gotten burnt when installing stables due to extension incompatibility issues. –  MiffTheFox Jul 8 '10 at 18:50
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5 Answers

up vote 27 down vote accepted

Yes, it is. This also works fine with the final release of Firefox 4. When you install, choose to customize the install. Then just make sure to select a different directory than where Firefox 3.6 is installed. I just did it yesterday, works fine! Firefox setup

If you want to be able to use both 3.6 and 4 Beta at the same time, you'll need to launch the 2nd one you open with the -no-remote command line, and specify a different user profile (can't open the same user profile twice at the same time). For more details on that, see Firefox command line arguments.

Important: This does not work when using Firefox Portable, it does not recognize the -no-remote switch.

Update: If you want to keep separate profiles for your stable and beta installations, create two different profiles. Start "<path to firefox>\firefox.exe" -ProfileManager. Your existing profile will already be there ("default"). Create a new profile (call it "testing" or whatever), then choose that.

profile editor

If you want Firefox to choose a specific profile for a specific installation every time you open it, you can modify the shortcuts to specify a profile. Change it to "<path to firefox>\firefox.exe" -P "Profile Name". This is case sensitive. It will then always open that profile. You could also just uncheck the box for "don't ask at startup" and choose yourself every time you start.

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But this still use same settings addons and history. I trid n-remote option it does not open up new instance of 4beta. –  Sharique Jul 14 '10 at 5:07
    
See the information I added about profiles. Using that with no-remote should let you choose multiple profiles and multiple sessions at once. –  nhinkle Jul 14 '10 at 5:25
    
no-remote open up existing (3.6) firefox,although no-remote with -p open up 4beta. –  Sharique Jul 14 '10 at 6:13
    
Are you sure you're typing firefox.exe -no-remote, not firefox.exe no-remote? You need to have the first dash. Also make sure you're using the path to the right installation and not getting those confused. Check those and it ought to work. –  nhinkle Jul 14 '10 at 6:16
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Using firefox portable might be your issue. I'm not sure if it has the same command line parameters as regular firefox. Try it with a regular local installation of each browser. –  nhinkle Jul 14 '10 at 6:46
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There are portable versions of Firefox here:

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This is the best way, as per my experience. –  Sharique Jul 14 '10 at 5:06
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If you are on a Mac, just rename the app before copying it to Applications.

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You'll need to be sure the beta doesn't clobber your profile folder though, right? –  Peter Murray Jul 7 '10 at 22:17
    
Both versions of Firefox will use the same Firefox profile, so you'll need to split the profile as well. –  Stefan Lasiewski Oct 5 '10 at 22:50
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Perhaps gross overkill for your particular application, but app developers will spin up a new VM for each version of the browser (in order to eliminate conflicts). VirtualBox and VMWare are 2 popular choices.

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No you cannot!!

At least it didn't work a few weeks ago when I tried. Next time I started Firefox 3 the toolbars were messed up. The reload button was moved to the right side of the address bar just like in Internet Explorer.

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protected by Diago Dec 13 '10 at 11:26

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