Running Firefox 2 and 3 simultaneously

As web developers we are always testing and re-testing our work in the latest browsers. As the release for Firefox 3 becomes imminent it is crucial to test everything while still being able to work since FF3 is not out of beta yet.

We have compiled a step by step guide to running both Firefox 2 and Firefox 3 simultaneously on both OS X and Windows. All OS X commands below can be run in the Terminal and all PC commands can be run from the Start->Run window.

Most of your extensions will not work in FF3 thus requiring FF2 to still be installed with full extension support to fall back on.

Although this tutorial is straight forward BACK UP your current profile before you start. Your profile is located at:

~/Library/Application Support/Firefox/Profiles/xxxxxxxx.default/

C:\Documents and Settings\[User Name]\Application Data\Mozilla\Firefox\Profiles\
C:\Users\[User Name]\AppData\Roaming\Mozilla\

1. Create a new profile

This can be done while Firefox 2 is still open. I suggest leaving it open just to verify your FF2 will stay in tact.

/Applications/ -profilemanager -no-remote

"C:\Program Files\Mozilla Firefox\firefox.exe" -profilemanager -no-remote


2. Install Firefox 3

Download the latest beta and make sure you install it to a separate directory than FF2. Remember DO NOT run FF3 after the install.


C:\Program Files\Mozilla Firefox 3 Beta 3\


3. Startup Firefox 3 and force the new profile

Force FF3 to use the newly created profile to keep all your bookmarks, extensions and themes separate. Most of the extensions and themes will not load in the new beta. Replace the “alpha” in the commands below with the name of the new profile you created in step 1.

~/Applications/ -P alpha -no-remote &

"C:\Program Files\Mozilla Firefox 3 Beta 3\firefox.exe" -P alpha -no-remote

4. Create a permanent shortcut to run the alpha release.



  1. Make sure Apple Script is in the system menu, Applications/AppleScript Utility
  2. Run the Apple Script Editor in Applications/AppleScript folder
  3. Paste in this code but replace the directory and the profile name

    do shell script "~/Applications/ -P alpha -no-remote &"

  4. Save the file to ~/Library/Scripts folder and name it something like “Firefox 3”
  5. To run the script in the menu bar click the script icon and click on “Firefox 3”, it should load side by side with FF2


  1. Create a new shortcut on the desktop pointing to the Firefox 3 installation
  2. Right click on it and go to Properties
  3. In the attributes section add in "-P alpha -no-remote" without the quotes after the quoted directory
  4. Click Apply and the shortcut should now run FF3 with the new alpha profile side by side FF2


You are now all set to test in Firefox 3 while still running Firefox 2 for every day work.