The Tor project just released version 3.5 of the TorBrowserBundle (TBB). Previous versions were based on Firefox 17 ESR and needed a legacy extension. The current TBB is based on Firefox 24 ESR and that seems to work with the current version of the 1P for Windows Firefox extension (I have v. 3.9.20). So that's good news!
Note that like TBB 3.0, it still requires making the hardlinks to glue the extension between TBB and standard Firefox as described in another post.