Rated 5 out of 5 stars

Versions 3.3 and 3.31b1 don't work in my Thunderbird. When I try to open the extension's options, I got the error message: "XUL syntax analyses error: undefined entity in chrome://tbrowse/content/tbrowsesettings.xul
Line 50, Symbol 14:

The & sign is marked as wrong.

This review is for a previous version of the add-on (3.3). 

They are malformed. Install beta 2 for 3.3.1, it will fix your issue.