Mozilla makes all old versions available for download, right back to version 0.x. The latest 'old' version can always be found at:
Hope this helps,
I downloaded the Firefox 3.5, which installed over my previous version, but it's giving me problems, so I want to go back to the older version that worked just fine.
Unfortunately, uninstalling 3.5 got rid of all of both versions, and I can't find the download for the older version.
Any suggestions on where to look for it?