JMurr, welcome to the forums.
If you still have your old Windows install with Firefox on it, here is something to try,
1. go to "C:\Users\Your Name\AppData\Roaming\Mozilla" if it is on Vista or 7, or "C:\Documents and Settings\Your Name\Application Data\Mozilla"; and copy the entire Mozilla folder.
2. Go to "C:\Users\Your Name\AppData\Roaming" and delete the existing Mozilla folder
3. Transfer the copy you made over to your new Windows install and put it in the appropriate location, "C:\Users\Your Name\AppData\Roaming".
I have been doing the above for so long now that I have pretty much been using the same profile in Firefox for the last 3-4 years with no problems. On a clean windows install once Firefox is installed I put the above in the right place, open Firefox and it is just like it was. Never used/tried MozBackup or any other 3rd party backup, just the above.
P.S. It also works with Thunderbird.