Great addon. Very useful and easy to use. Only annoying thing is none of your system fonts like Calibri, Segoe UI, Trebuchet MS, Tahoma, etc. show up in the list of fonts so you have to manually type them out to add them but I'm not sure if the filename in the font folder is the correct name or the font names in Firefox options. I wish you could simply scan the font folder to add the fonts or at the very least give some indication you typed the right name.

But it's still an excellent addon. I use this with Zoom Page WE (to change the font size) and it works beautifully.

Edit: I just noticed when you type out the correct name in the search box the name will change to that font style. So there is a visual indicator to let you know it's the right name.