Shareaholic is a free Firefox add-on that allows you to email and bookmark web pages just by clicking a button inside Firefox.
It completely integrates itself within Firefox, as big green-RSS-logo button: when you click the button a drop down menu will show you all the social bookmarking services to which you can save the page you’re browsing (services include Digg, Delicious, Google Bookmarks, Twitter, and more…), offering information about how many times that page has been dugg or saved to del.icio.us. Plus, you can also email that particular page to anyone, right from inside the menu.
Shareaholic also has a Customize menu, that lets you select which services you want included in your list, and a Community Links menu: as the name says, this menu shows you all the recent websites that people are bookmarking in real-time.
The extension is completely free to download and use.
Link: http://shareaholic.com/
Update: Shareaholic now supports FoxieWire, the best social platform to share all of your Firefox news.