Built this in 3 hours since I had so many ADHD friends saying Bionic Reading helped them immensely. It's slapdash, doesn't work on all webpages, and generally unrefined, but it does the job.
EDIT: put a few more hours in, it now works for basically every static content page I've tested. It breaks functionality on highly dynamic pages like twitter, since it edits the DOM, but even there it properly modifies the text.
EDIT2: and now no longer breaks buttons and similar! Honestly really happy with this.