I really, really, really wish I could rate it higher. Prior to November/October this would easily be a 4 or 5 star rating. Since then, however, there's been noticeable slowing in my system to the point that I can't use FF while this extension is enabled. I don't know if this add-on changed or if FF did, but I went from using this extension 24/7 to only using it when my eyes are really hurting and, even then, while needing to weigh out what speed I need pages to work at. The extension has crashed my browser multiple times and has been a disappointment since. I'll amend this if it's fixed, but for now I can't recommend this extension :(