I concur with others posting about problems with this extension. The switching content between tabs, even across multiple regular and private browsing windows, is a show stopper!!!!! This extension is unusable for that reason, even though it has some other good features. I also suspect the extension is responsible for reversing the order of tabs on Firefox startup, another very annoying problem! I might consider reinstalling the extension if these problems are fixed and the author adds the ability to delete individual tabs prior to restoring windows.

http://forums.mozillazine.org/viewtopic.php?f=38&t=3041078&p=14805909#p14805909