Wow, this made my day (above)! Our little Add-on for Firefox is the #5 shared add-on on Mozilla.com. The best part is that we have over 150 services integrated in the Add-on... many of which are my favorites.
This is what my AddThis Firefox menu looks like (above). The ones I use the most are Gmail, Facebook, and Tumblr. I really like Amazon, but it's not really social. I wish there was a service out there that makes shopping with friends online easier. It'd be cool to have a service that's called "buy later" (just creates a social wishlist of things you want). I've tried ThisNext, but none of my other friends are using it. *sigh*.
Try AddThis for Firefox