The add-on for Firefox will continually run in a sidebar, and can be activated by selecting a chunk of text and dragging it over to the sidebar.  You then get tons of information about that person, place, thing you are searching about.  When dropping text into Juice, we’ll try to understand its meaning and serve you with context-relevant information.

How can you turn the sidebar on and off?  After installing Juice, you get a new toolbar button to do just that (or setup your own hotkey).  You can save things for later too.

All in all, Juice is well worth trying out if you need a new way (or perhaps better way) to search for basic information intelligently.