I've just found a nifty Firefox extension that drastically cuts down Firefox's memory usage. If, like me, you have several instances of Firefox open, and multiple tabs open in each instance, you'll find Memory Fox gives you back quite a bit of RAM.
To check your current memory usage, open up your Windows Task Manager and locate Firefox on the Processes tab. Make a note of how much memory it's using and note how many tabs you have open. Install Memory Fox, and restart Firefox. After restarting Firefox you should have the same number of tabs open as before. Enable Memory Fox and check the memory usage again: you should see a significant difference. I had four tabs open and Firefox was using 300,000K (around 300MB) of memory. After installing MemoryFox and restarting the browser I checked again and memory usage had dropped to around 90MB!
Read more about it here on MakeUseOf.com: http://www.makeuseof.com/tag/memory-fox-helps-tame-memory-usage-in-firefox/
Currently, there's a minor snag when installing the extension. Instead of installing as it should, there's a minor glitch which results in an error message. After ticking the "install experimental add-on box" and clicking the "install button", an error message pops up.
Just select the line of code and paste it into the browser's address bar; delete the "?confirmed" part and press return and the extension will install. Alternatively, use this: https://addons.mozilla.org/en-US/firefox/downloads/file/72813/memory_fox-1.03-fx-win.xp
