Firefox Memory Usage Through the Roof

Firefox's memory usage has just gone nuts lately on my work machine, approaching 1 Gigabyte of RAM usage:

I have no idea what is causing it. The most likely culprit is either some javascript leak on a page I leave open all the time (like GMail for instance) or a leaky extension/add-on. Here are the add-ons that I use:

My suspicion is that it might be Fasterfox that is causing the problem. I will disable it and see what happens over the next few days.