Rated 5 out of 5 stars
I have been using this for over two weeks now. And as someone who makes heavy use of tabs, I find this to have reduced my FF memory consumption by around 80%!
The only additional setting that pushed this down further to around 85% is this setting - "When I don't visit a tab for a while" = "Unload it after" .. "20 minutes".
It is now a part of my permanent add-ons collection (the only other two are Adblockplus and XMarks).