Well integrated Rated 5 out of 5 stars

Not bad for a first version!
It does what it's name promises. It gives you information about the fonts used inside a page or the current selection.
Unfortunately I don't see any additional info to the WOFF files on the pages I tested this extension with.

This review is for a previous version of the add-on (0.1). 

Many authors/vendors currently use WOFF files with no added metadata, in which case nothing will be displayed. If you try Fontdeck's site at http://fontdeck.com, for example, you should see a number of WOFF files that do have metadata attached.

(Now that it's possible for users to view this data, I hope this will give an added incentive for font vendors to include it.)