Try going to about:memory to see if some tab is taking up a lot of memory. I've got this CI system where if I leave it open overnight it takes a gig or two and

Try going to about:memory to see if some tab is taking up a lot of memory. I've got this CI system where if I leave it open overnight it takes a gig or two and makes the browser unusable (Firefox and Chrome; it's a problem with DOM elements). If your GM scripts retain DOM elements for a long time (and the tabs aren't closed) that might be an issue too.