Hi. It's a little hard for me to understand why the complain having in mind that the addon is specifically built for manual saving of sessions AS BOOKMARKS. There's no way that would be automatically because the addon would make firefox unresponsive every 10 seconds otherwise. Saving tens of bookmarks or even hundred is not acceptable for performance reasons. Yes, the addon has another small feature that saves in background everything once ever 15 seconds (or whatever you set), but that's clearly not something full featured and can't be compared with an auto-save session addon. I totally understand that the addon may not be for everyone, but I'm not even trying to promote it to those that want auto-saving :|. The description says that "you can save sessions as bookmarks" not that they are automatically saved.
This addon is intended for those that want control over what and when they want things to be saved and on top of that is made for management using the bookmark system. Don't want to be mean, but I'm not trying to sell the addon as what it's not, so giving it a 1 star for something that is not even suppose to be doing is not really ok.