Can't get Firefox to recognize backed-up profile on new computer.

I've just installed a new copy of Windows and I want to transfer my old profile to this install of Firefox. I'm running Firefox 4 on my new computer and my old one. I copied the xxxxxx.user folder from my AppData/Local/Mozilla/Profiles folder onto my flash drive. I then ran the profile manager on my new computer and created a new profile. Finally, I copied the contents of my original xxxxxx.user folder into the new xxxxxx.user folder (I did not just copy the old profile folder into the Profile folder of the new Firefox install, just the data). When I loaded Firefox though, it looks just as if I had installed it fresh and hadn't done anything with it yet. I really would like to have my browsing history on this new PC. Thanks.