Running multiple Firefox versions side by side on Windows

Whenever you upgrade your Firefox, the new version will overwrite the previous one. If you want to open multiple Firefox versions side by side, here's my way :

  • First, uninstall all your previous Firefox installation(s). Make sure to backup any important data beforehand (I personnaly use MozBackup to do that).
  • Then install the latest available stable version. This will be the main Firefox version, the one you'll be using on your dayjob and the one you'll always update.
  • Now run the Firefox ProfileManager. To do that, create a shortcut to your firefox.exe file, then edit this shortcut. In the "Target" field, add -Profilemanager.

My field looks like : "C:\Program Files\Internet\Firefox\firefox.exe" -Profilemanager

  • You now have to create one new profile for each FF version you plan on testing. Give them meaningful names. I named mine "FF3.0".
  • Now download the corresponding Firefox version from
  • Do not install it, but extract its content (using a archiving tool like winrar or 7-zip) in a tmp directory. Remove the optionaldirectory as well as removed-files.log and setup.exe.
  • Copy the content of localized/ into nonlocalized/ (overwrite files if asked).
  • You can now rename the nonlocalized/ directory and move it around on your hard drive. I renamed mine to Firefox 3.0/ and put it alongside the main Firefox, in C:\Program Files\Internet\Firefox 3.0\

  • Create a shortcut to the firefox.exe file in this directory and edit the target field. This time, we have to specify which profile to use. Just add -P "FF3.0" -no- remote in the target field.

Mine now looks like C:\Program Files\Internet\Firefox 3.0\firefox.exe" -P "FF3.0" -no-remote

That's it.

Now, just run your classic Firefox shortcut to open the most up to date Firefox version, and use the custom shortcuts to open previous versions.

I personnaly also rename the different firefox.exe to firefox30.exe, or firefox35.exe to more easily spot them in the taskmanager.

I also edit each .exe with ResHack to change their taskbar icons. I haven't yet managed to change their title.

Edit : Now I can't open .html files directly from the explorer nor follow links from my IM. I still don't know exactly what of the steps above caused that.

Tags : #windows #multiple #firefox

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