Here's a screenshot: http://i56.tinypic.com/10fqtd3.png When tabs are opened, Firefox requests and is allocated memory (as expected). However, when the tab is closed, memory is not freed up. I've tried running with all extensions, themes, plug-ins, and add-ons disabled. I've gone so far as to try a freshly-imaged machine with nothing else installed but Windows (no Flash player, no Java, no antivirus software, no audio/video software). I've tried multiple machines built with different OS installations. None of this changes what happens in any way. It's happened since I first installed Firefox 3.0, and I've tried each subsequent revision. I don't have many tabs open at once (no more than 30-50 tabs), but each one is often the product of a long chain of links. This suggested the culprit might be the memory cache, but even if I turn that off, there's no change. Having more tabs open at once just makes the problem happen that much faster, proportional to how many tabs are open. Eventually, Firefox grows to unsustainable size, as above. At this footprint, Firefox is grossly unstable and will slow to a crawl, despite the system having 8GB of physical RAM. It will either crash on its own when the footprint exceeds roughly 1.5GB, or it will need to be terminated from the task manager and restarted before it can be used properly. I've tried tips from all manner of articles, such as Safe Mode, disabling/shrinking the memory cache, changing browser.sessionhistory.max_total_viewers, config.trim_on_minimize, nothing helps. Searching for [http://www.google.com/search?q=firefox+memory+leak&hl=en&num=10&lr=&ft=i&cr=&tbs=qdr%3Ay,qdr:m firefox memory leak] within the last month yields 272,000 results, so I don't think I'm alone. http://www.google.com/search?q=firefox+memory+leak&hl=en&num=10&lr=&ft=i&cr=&tbs=qdr%3Ay,qdr:m