I would like to know of addons which actually enhance firefox's performance, both intentionally and unintentionally. I find that firefox tends to have major performance issues with certain websites. These websites tend to have a fair amount of javascript and css, and probably a large dom tree which may even be growing dynamically through javascript too. The worse offenders are those with heavy javascript, use heavy facebook integration, websites with non performant javascript, excessive javascript and websites with too many advertisements.