Windows only: Eager to check out all the new hotness in the Firefox 3 beta but don’t want to scuff up your perfect Firefox 2 setup? Web log Digital Inspiration points to an elegant solution:
1. Download the Firefox 3 Portable edition.
2. Extract this Firefox 3 installer to some new folder like C:\Firefox3
3. Close your Firefox 2 browser and run the FirefoxPortable.exe file available in the above folder. That’s it.
This worked perfectly for me, but it’s probably a good idea to back up your Firefox 2 user profile, in case you accidentally open them both or something goes awry. For tips on doing that and more, check out Gina’s guide to managing multiple profiles.