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HOWTO run multiple versions of Firefox side-by-side on Mac OS X Lion


Cross-browser testing is pretty essential when developing web sites. Most of the bugs you need to fix are probably in older versions of Internet Explorer. Both Chrome and Firefox have a very fast release cycle, where new versions are released every six weeks or so.

However, there are still many people using the older 3.6 version of Firefox. Firefox 3.6 has a few bugs, and because of its big installed base you probably need to run some tests on it as well.

There’s a problem here: Firefox doesn’t like it when two different versions are run side-by-side. Fortunately there are a few tricks you can use to make this happen. This should also work on Snow Leopard, provided you have at least 10.6.2, because the --args parameter was introduced in that version.

  1. Download the Firefox 3.6 release from
  2. Unzip and mount the DMG file.
  3. Drag the file from the DMG to your Desktop instead of to the Applications folder.
  4. Rename the .app to ‘’ and move it to your /Applications folder
  5. Run this command from a Terminal (found in /Applications/Utilities):
    /Applications/ -ProfileManager
  6. Add a new account. Call it ‘test’.
  7. Run Automator. From the ‘Choose a type for your document’ menu, select ‘Application’.
  8. Drag ‘Run Shell Script’ to the action area.
  9. In the content area (where ‘cat’ is displayed) copy-paste this line:
    open /Applications/ --args -P test
  10. Save the document to /Applications as ‘Firefox 3.6’
  11. Drag ‘Firefox 3.6’ application from the Applications folder to your dock for fast access.
  12. You’re done!

For a nice icon to differentiate your current Firefox version with the old one get the full resolution PNG from above this article right here. Open it in preview, select all (Cmd-A) and press copy (Cmd-C). Open up the Automator .app by right-clicking and selecting ‘Get info’ or hitting Cmd-I. Select the icon in the topleft corner so that it is outlined and press Paste (Cmd-V).

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