Appréciable ! Rated 4 out of 5 stars

Very simple and yet great addon for me. It sorts the bookmarks just as expected without messing anything up, except for the bookmarks toolbar which is sorted right after install and restart of firefox (see Carlo Santucci's comment).
Thanks to the developer !

This review is for a previous version of the add-on (1.6.1-signed). 

In version 2.0.2, the extension ask the user a confirmation before activating the auto sorting option.