Oops!
The SessionSaver plugin for Firefox only works if you re-open Firefox the normal way; if you close it and then re-open it by clicking a link in your email, it doesn’t restore anything you were working on last session. I just found this out the hard way – I have had approximately 50 tabs open for several weeks at this point, and SessionSavor has been working great. Due to Firefox’s caching silliness, I keep needing to close the program, since after a while it eats up all of my memory, but as I said, this has not been a problem at all until I just clicked a link a few minutes ago. Now, all my previous tabs are gone. Lesson learned, but I’d have preferred to learn it a different way.