There are a few steps to take due to potential problems with installing an older version.

1/ See Tietojen varmuuskopiointi - Always a good idea to back up your user information first.

2/ Download the latest version of Firefox 2 from http://www.mozilla.com/en-US/firefox/all-older.html

3/ Uninstall Firefox, if you are using the Firefox 3 uninstaller when asked say no to "Remove my Firefox personal data and customizations"

4/ Make sure that there are no files left in the installation folder, default location C:\Program Files\Mozilla Firefox

5/ Go to your profile folder.

Firefox 3 would have converted your profile to the Firefox 3 format by creating some new files. You should delete these files along with some others to avoid having problems either now or when you decide to update to Firefox 3 at a later date.

Delete the following files:

• content-prefs.sqlite
• places.sqlite
• downloads.sqlite
• cookies.sqlite
• permissions.sqlite
• formhistory.sqlite
• signons3.txt (if the profile folder does not contain a file called signons2.txt you can also remove key3.db)
• urlcalssifier3.txt
• extensions.cache
• extensions.rdf
• extensions.ini
• I also recommend deleting localstore.rdf, you will need to reset your toolbar customizations.

6/ Install Firefox 2

As an alternative to step 5 you can, after installing Firefox 2, create a new profile, then copy important data to it.
See Creating a new Firefox profile on Windows - MozillaZine Knowledge Base
Once the new profile is created, see recovering important data from an old profile.

My computer has started to act very weird since i installed Firefox 3 so i am rolling back as well.

Mozilla really should have done some more testing before releasing firefox 3.

Ruining their reputation.

I can't stand the new auto-fill in the address bar, I'm rolling back.

I can't stand the 3.0.1 version!

Gimme back the old version that was so much better! The address bar makes little to no sense. That's what I hate the most. I really hate that address bar. It's distracting and slower than what I used to have, and it takes me LONGER to go to where I want. Ugh.

I'm very disappointed.

Will now try to roll back.

I hate the smart location bar also. I have a real problem with not having my old address bar - all of my addresses are gone. Plus the address bar is getting clogged up with sites that are on my links bar. That never happened with the old address bar. Rolling back to an earlier version and learned my lesson about installing updated versions of the browser that I loved. This is almost enough to drive me back to Microsoft IE. Almost ....

I would like to hear from anyone that had success in rolling back to an earlier version. I dread having to re-bookmark all of my sites so am waiting to hear if the above instructions helped or not.