The best sessions manager Rated 5 out of 5 stars

Works very well, dev.builds are always available, has a truck load of options, easy to follow documentation with illustrations, change logs, well supported by a very responsive developer (just read the ongoing thread on Mozillazine forum).
Everything one would wish for in an extension.

This review is for a previous version of the add-on (0.7.9.5.1-signed).