Allows connections through SOCKS or HTTPS proxy servers.
Extension for Firefox that allows you to manage multiple email accounts in Gmail.
Firefox extension that displays relevant Wikipedia articles alongside your Google search results.
Utility that displays the details of all browser add-ons/plugins installed on your system.
Dooble, the scientific browser.

Don't have the patience to wait and type unreadable codes on sites like Rapidshare and Megaupload?