Even after having a massive 4GB RAM, of which a good share is always free, my Firefox used to be slow. Can’t blame it completely; 40+ tabs and a couple of dozens of plugins would make anything slow, but closing down the tabs wouldn’t solve the problem.
The easiest way out was restarting Firefox. Restarting is not a big deal, if you have free bandwidth and have the habit of completing everything you started. That doesn’t describe me at all.
Luckily, I stumbled over a amazing plugin called RAMBack.
RAMBack is a simple plugin that does nothing but clear the RAM that’s being used by closed tabs and unused pages. The plugin will add a menu item ‘Clear Caches’ into the Tools menu (see the snapshot). When clicked, it will do its job.
I had been using RAMBack for over a month on FF 3.5.1, so far so good.