I have to admit that while I do not agree with every decision Mozilla makes in regards to Firefox, I can't really complain about the web browser's performance on my system. It is as stable as it gets, does not use too much memory or cpu, and is a pleasure to work with. While I do my best o ensure that, for instance by running it without plugins and with NoScript, it is the complete package that makes the difference.
This was not always the case, especially during the Firefox 4 days when the browser started to eat memory like crazy. If you are running Firefox currently and notice it slowing down considerable over time or right away, I suggest you try the following fixes to resolve the issue.