OS X: Install and Run Firefox 3 and Firefox 4 on the Same Computer

   Posted June 29, 2010 by David Kirk in Mozilla Firefox

Are you dying to try out firefox 4 but not ready to give up firefox 3? You can run them both safely on your apple os x system. Here is how to do it. Updated for latest versions of firefox.

This technique will work for running any prior versions of firefox. Previously, this tutorial covered running Firefox 2 and 3 concurrently. This has now been updated to cover firefox 3 and 4.

When you install firefox 4 normally in os x, the process will overwrite your firefox 3 installation. Especially during the beta phase, you may not want to completely upgrade just yet. Here is how you can have firefox 4 and firefox 3 on your system.

1. Download firefox 4
2. Click on it to start the installation process
3. Instead of dragging the firefox icon to your application folder, drag it to the desktop top.
4. Select the firefox icon and press enter. Rename the firefox application to something more appropriate. I used firefox_beta, for example.
5. Drag the renamed application to the application folder.
6. Run firefox 4.

If you want to uninstall firefox 3 and revert back to firefox 2, just drag the firefox 3 icon to the trash.

Next, you will want to protect your firefox 3 profile. Create a new profile before running firefox 4.

1. Open the Terminal
2. type cd /Applications/Firefox.app/Contents/MacOS
3. type to run the ProfileManager: ./firefox-bin -ProfileManager
4. Create a new Profile and select it.

profile manager firefox 3

Here is an example of them running side-by-side:

firefox 3 and firefox 4

Now all your firefox installations will run the new profile. If you decide you no longer want to run firefox 4, then repeat the process to revert your profile back to your default before you delete firefox 3. If you want to continue to run firefox 4 with your old profile (and bookmarks, etc), then switch the profile over to your old default profile.


About David Kirk

David Kirk is one of the original founders of tech-recipes and is currently serving as editor-in-chief. Not only has he been crafting tutorials for over ten years, but in his other life he also enjoys taking care of critically ill patients as an ICU physician.
View more articles by David Kirk

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  • http://www.tech-recipes.com David Kirk – Founder/Editor

    You can find the appropriate nightly build of firefox 4.0 here for now…


  • http://www.tech-recipes.com David Kirk – Founder/Editor

    Previously this tutorial described running firefox 2 and firefox 3 concurrently; however, since the directions are basically the same, I just updated this post with the latest versions.

  • Liberalmark

    Great solution—thanks! However, you note “run firefox 4” in step 6. Then, a couple paragraphs later, you mention something that needs to be done before you run v4. I think that’s a pretty important note you miss up top.

  • jeff

    It’s amazing that these instructions aren’t easier to find given how many people must need to do this. Sadly the instructions out there are pretty skimpy in detail these are the best I’ve found but are still missing many critical stepsfor example firefox must be closed to get into the profiles area in the mac terminal window and david you are still qujite confusing in your presentation
    this link will give you some more complete info so that you can do this without guessing what you are doing.

    Oddly the above link seemed to only open properly in chrome not safari. “very wierd” In Safari it showed up as some kind of PC gibberish. It opend in a firefox browser as well but you need to keep firefox closed to get into profile manager so you need to use another browser if you want to follow along. Between Dave’s instructions and the mozilla profile link above you should be able to pull this off with no hitches