A good way to test Firefox 3 without having to install it over your precious Firefox 2 client is to download and run the Firefox 3 portable version which comes with all features of Firefox 3 but does not tamper with previous versions of Firefox in any way. The portable client uses its own profile which is located in the same directory structure as the program’s files.
It pretty much does everything that Firefox 3 can do as well. It is possible to install extensions and themes for instance. Bookmarks can best be imported into the portable version. Just point it to your bookmarks.html file in your Firefox 2 profile folder.
It is even possible to run both the Firefox 3 portable version and another Firefox version at the same time. To do that you need to create another profile for the portable version. Head over to my article that explains how to
multiple Firefox profiles simultaneously.
Firefox 3 Final Portable