Search Keys is a great Firefox extension that lets you go to search results by pressing the number of the search result instead of clicking. For example, pressing 1 takes you to the first result. Hold Alt (Windows/Mac) or Ctrl (Linux) to open results in new tabs, or Shift to open results in new windows. More information here.

Search Keys supports Google, Google News, Google Groups, Google Desktop Search, and del.icio.us. Marc Abramowitz (Technical at Yahoo) provided a Friday Hack: Search Keys extension for Firefox and Yahoo! Search