Ubiquity takes language based instructions and turns them into action, right where you  need them to be.  This video goes a great job at explaining the add-on and showing it in action:

Ubiquity for Firefox from Aza Raskin on Vimeo.

Here are a few more tutorials to get you started:

• User Tutorial for Ubiquity
• Developer Tutorial for Ubiquity

The initial prototype is a little rough, and not ready for prime time yet.  It does show a lot of promise though, and with a little creativity this type of tool could go a long way.  Ubiquity looks to be another amazing tool to add to the many that have come out of Mozilla Labs.

Here is what Quick TransLation looks like in action:

Of course that is the English translation of an English word. The highlight is you can select from the status bar flag that is added the language you would like to read that definition in. If you spend your time reading a lot of content on the Web that is from another country, this extension would be a handy addon to make use of.