There is no reason, NO REASON that Firefox should eat up 1 GB of RAM.
Firefox caches images and rendered pages so that things happen reasonably fast. A 1000x1000 colur image at 24 bit is already 3M. There is no way a modern page with an image or two would fit in a few M.
Once you have 800 tabs loaded (something I tend to do) all running JS and using images all over the place, memory vanishes fast.
There are basically several problems. Yeah firefox isn't perfect and could do with some optimization. But, many websites do pointless bloaty stuff and require scads of JS and huge images just to show some text. And then there's the browsing habits.
These days I run with NoScript, and a tab unloader, and I'm picky what scripts I allow. It makes firefox usable on my 1GB netbook. It's taking up 176M at the moment. Actually it's got a bit better recently. Even with those it needed restarting to clear the ram, but now it runs substantially longer.