It's described as a sort of dynamic mashup capability for the Firefox browser, or web application hybrid to put it in Wikipedia terms, enabling you to combine data and applications from more than one source into a single integrated tool. This would allow you to do much more inside Firefox than the vanilla fixed-function browsing now afforded.

It's very much an experiment in its earliest stages, but looking at the video will give you a feel for its ultimate potential.

As per usual for Mozilla, the code underlying Ubiquity is being released as open source software under the the GPL/MPL/LGPL tri-license.

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