Rated 5 out of 5 stars

@ Mskadu... niceshorts is correct! The easiest way to fix this is to a) uninstall your current, TB 3.1.x-incompatible version of Quicktext, b) head over to the author's homepage and download the current version (more on that below); c) install the fresh .xpi in TB and restart.

Note: the author probably should have renamed the current version from his website 0.9.10.2 or the like, as the "old" 0.9.10.1 is in fact incompatible with 3.1.x, but the "new" version is. For more information, see this thread: http://extensions.hesslow.se/forum/thread/391/Thunderbird+3.1/

Good luck!

This review is for a previous version of the add-on (0.9.10.1).