ThunderBrowse 3.7 working fine here Rated 5 out of 5 stars

ThunderBrowse 3.7 + Thunderbird 5 appears to us as ready, working, and stable. 3.7 appears under intense usage totally compatible with Thunderbird 5, and runs superbly on our multiple Win 7 32 and 64bit systems. NOTE!: ThunderBrowse + Thunderbird 5 works as expected in our systems here. Message pane works flawlessly, as do other displays. SOME users report Message pane problems, so your mileage may vary.

You can get 3.7 without waiting for Mozilla OK at:https://addons.mozilla.org/en-US/thunderbird/addon/thunderbrowse/versions/

This review is for a previous version of the add-on (3.3.5).  This user has other reviews of this add-on.