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I've been reading this:

But it looks like it only applies to running multiple versions of Firefox when it's Firefox 4.

I need to run Firefox but it seems like a lot of my clients are still running versions of Firefox 3 (is this an operating system issue? Doesn't Firefox auto-update?) so I need to run 3 plus the latest version to troubleshoot some css issues...

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migrated from Sep 14 '12 at 18:03

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What operating system? – Su' Sep 14 '12 at 17:59
Mountain Lion, sorry I forgot to add that. – nicole Sep 14 '12 at 18:03
FF can auto-update, but the users can turn automatic updating off if they want. And yes, older versions of the OS can't run the very latest Firefoxes; for instance FF 15.0 requires MacOS 10.5 or higher. By the way, I'm pretty sure the way to run multiple FFs (in the link you provided) works for other versions as well. – Mr Lister Sep 14 '12 at 19:00
Also note that Firefox will auto-update when you launch it so if you want to turn it off you should disable your internet connection the first time you launch it so you can get into the settings before it tries. Had this problem before. – ioSamurai Sep 14 '12 at 19:53

The easiest way for testing is to get the Portable Apps Edition of Firefox for the various versions. This avoids profile and addon conflicts.

They only list a few of the older versions on the website, for rest you have to goto the Firefox section of their SourceForge project.

In the same folder as the FirefoxPortable.exe, create a file called FirefoxPortable.ini and add the lines:


To run more than one edition at the same time and remove the splash screen delay.

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You may be also interested in online services like BrowserShots or Adobe BrowserLab, which provides web page view for many different OS-browser-version combinations...

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