I’m pretty sure that reading YouTube comments actually gives you cancer. At the very least, it will cause you to seriously question your faith in humanity. Thankfully, TannerStoke has the answer.
The full list of Firefox extensions that I consider absolutely mandatory. All of these work with FF 2, and many work with older versions. All but one or two have also been updated to work with FF 3. (List last updated Aug 26, 2008.)