FireFox Bug running Google Docs?

I've noticed a disturbing pattern when running Google Docs on FireFox. I typically run 2 separate gdoc gmail account tabs and 2 separate calendar tabs as well as other tabs for my web app etc. What consistently happens is that FF uses increasing amounts of memory. By the time it hits 1gig of memory used, the response time is amazingly slow.

As an experiment, I tried running just the gmail and calendar on IE, and was shocked not to find a similar problem. Is there some kind of javascript bug running on Firefox? Or could this be related to Firebug and Yslow running on the browser at the same time? Anyone have a similar problem?