Note: This review addresses v1.4.1 of the software.
The Shareaholic extension for Firefox adds a button between the home button and the address field. Click that button, and you get quick access to sharing your current site through a variety of social networking services, including del.icio.us, Digg, Facebook, StumbleUpon and others.
You can also quickly e-mail links using Bzzster, and see how many times a page has been Dugg or saved to del.icio.us. There are currently 21 different sites and services you can select to show up in the addon's drop-down list.
If you're an inveterate social networker, Shareaholic can make it easier and faster for you to share all those great sites you find.
Note: The download link takes you to the Mozilla addon page, where you can automatically install the file into your browser.