Incredible addon! Firefox have to be impremented in default. Rated 5 out of 5 stars
It's a must! and being the best, paired with "Tab group manager" to organize the tabs with "group tabs" and "tabs group", firefox still startup fast when "Don't load tabs untill selected" enabled.
Best of all, It's keeping pace with firefox update (currently I'm using 10.0b1), and work well with them.