Firefox frequently uses 1 GB of memory on me. I make a habit of closing it every now and then. Very annoying. A web browser, need 1 gigabyte of memory? REALLY?
Actually, it does. The reason why browsers use so much memory is that they cache the history of
each tab. Right now I probably have 20 tabs open and each tab probably had around 3 previous webpages open, so those are all stored in memory for faster back<->forward action.
But with Firefox, you also need to consider that Firefox.exe is not the only thing to look at. plugin-container.exe is the program is uses to contain plugins so them crashing doesn't bring down the browser. Right now I'm using 618MB of memory with Firefox and 595MB of memory with the Plugin Container.
The biggest problem I notice with FF is that if you leave it open for awhile, it is absolutely awful with Flash videos. The video begins to exhibit "micro-pauses" (only affecting the video, not the audio) and this problem only goes away when you close Firefox and reopen it. Because of this, I sometimes have to open Netflix in Chrome because FF will simply do those micro-pauses throughout an entire TV show or movie.