I'm currently running version 8.0 or Firefox, but this has been happening for a while. Firefox absolutely eats up my memory. If I let it go a couple of days up, it will consume over a gigabyte of memory just in the main firefox.exe process, and the plugin container will take at least 250MB. I'm not sure exactly what is causing this. Granted, I routinely keep about 10-12 tabs open and one of them is always Grooveshark, a streaming music service. Would this be enough to drive up the memory usage that much?