Rated 5 out of 5 stars

My earlier comment noted a conflict with Personal Menu, which I attributed to UnMHT. I was wrong. After developing problems with the 3.5 RCs, I learned the problem was with Personal Menu itself. Uninstalled the stinker, and now UnMHT (and all my other extensions) are working just fine.

This review is for a previous version of the add-on (5.2.0.1).