Mozilla Ubiquity

Although it's only at release 0.1, Mozilla Labs' Ubiquity promises to be a game-changer, and ensures that Firefox will continue to be my desktop browser for some time. One part Yubnub, one part Quicksilver, Ubiquity allows you to hit a key combination to bring up a command window where you can type abbreviated commands and get instant feedback. Some examples:

• map university of texas at austin (Brings up a Google map)
• youtube cookie monster (Displays video stills search-as-you-type, defaults to Youtube search results)
• g spinuzzi (Brings up Google search results for Spinuzzi)
• word-count (Counts number of words in your selection in the main Firefox window, or counts words that you type after the command on the command line)

The command list is fairly long, but it's also extensible, like Yubnub.