There's a new kid in town! Rated 5 out of 5 stars
UnloadTab is the "Up & Coming" answer to Firefox 8! I am thrilled that Mozilla finally listened to our howls about memory overload when feeding our multi-tab addiction. But still no ability to unload old tabs. Voila! -- "UnloadTab."
Bartab was working for me with FFx 7. However, when I upgraded to FFx 9 I was out of luck. I enabled it with Add-on Compatibility Reporter. But, alas, no options button in Bartab. Hunh???
So thanks for the great years of service, Bartab! 5 stars for our time together. It's been great.
Update: UnloadTab does not seem to free up memory when the tabs are unloaded. Not sure what's going on there.