I'VE BEEN LOOKING FOR THIS, I HAVE ADHD AND IT REALLY DOES HELP i'm seconding the open-source thingy! would be neat
also THIS WORKS WITH CHINESE/JAPANESE/KOREAN/THAI SCRIPTS! (a lot of things don't, sadly)
would be nice for it to work while inside text input fields too, and, hmm, while inside other extensions native browser pop-ups (not windows)?.. (think yomitan) something like that ( ᐛ )و

Integrates well with website fonts, doesn't cause strange spacing, is sufficiently configurable. Would be nice if it were open source.