>Firefox: Quite a few sites have their own "Share" buttons for social networks like Facebook and Twitter, but Firefox Extension F1 builds that functionality right into your browser, sending any link right to Facebook, Twitter, or Gmail.
If you're a compulsive link sharer, this extension is for you. With just a few clicks, you can share any link via your favourite social networking site. What's especially nice about the extension is that it's made specifically for those sites, so instead of just sending a link in bare (or worse, preconstructed) email or Twitter update, you can craft your own tweet, status update, or Gmail message around the link you want to share. It's another great way to socialize your browser without switching to something like RockMelt—just install the extension and go.
F1 is a free download, works wherever Firefox does.