Very useful. Strange this behavior isn't built in firefox. Rated 4 out of 5 stars
There are nitpicks that prevented me from giving it 4 stars.
1) The placement of the option in the main app menu.
Nothing should be below the 'exit' menu item.
2) The fonts are not ordered alphabetically in a single list.
There seems to be 2 lists of fonts, each sorted by name, one after the other. The first contains fonts like Andalus, ... Cambria, ... Lucida Bright, ... Times New Roman, the second contains Arial, Calibri, MS Sans Serif, Segoe UI, Tahoma, Verdana.
I couldn't figure out what separates these fonts. They are all windows 7 defaults, all are TrueType (none are OpenType), all are composed from several files (one for each style - regular, bold, italic, both).