StumbleUpon: "Discover great websites, videos, pictures and more — all according to your interests."

One of the top Firefox (and IE) extensions: StumbleUpon!

By the web site:
"Channel surf the internet for great websites, videos, pictures, games and more!
Get personalized recommendations according to your interests
Rate, review and share what you find
Keep an online history of the things you've Stumbled
No adware or spyware guaranteed."
And it's really true.

tag: StumbleUpon, free, Firefox, Internet Explorer, extension