Love this! Stumbled on it while prepping FF for 11/14/17 57 release. For the eyeball impaired (sure there's a better term...) it works like a charm. Not only the physical size of the characters, but 2 important factors. Contrast (that horrid grey stuff!) and the edge highlight. Latter is akin to the TrueType Font adjustment in Windows....sharpens the edges so characters appear more clean cut. The author can explain better, I just know what I see and like.

This is a true case of WYSIWYG! Make it your own!