Rated 3 out of 5 stars
Works well at reducing the RAM usage, however at a cost. When opening a new tab after Firefox was minimized, Firefox will hange while it retakes the RAM it wants.
If Firefox is idle, the RAM usage will drop to 30 to 50 MB. When Firefox is active the RAM rockets up. Without this addon the Firefox will slowly eat your RAM (even without any addon's installed). My Firefox will use up to 1.5GB of RAM. When Firefox gets to about 700MB of RAM, Firefox becomes 'sluggish'. With this addon, Firefox get up to about 500MB of RAM, even when active.
All in all, a good addon, however, restarting Firefox is the fastest way to reclaim the RAM Firefox wants.