Social Fixer for Facebook plugs into your browser and improves the existing Facebook.com web site. You get to pick which features you want to use:
Lifehacker , Kim Komando , Mashable , Ars Technica , The New York Times , MakeUseOf , CNet , Slashdot , ZDNet , PC Magazine , and more!
Built by a well-known and trusted javascript/social media expert. With well over a million downloads, it's one of the most popular Facebook extensions available.