Someone else mentioned a browser add-on that lets you modify fonts on a per-site basis, but there are other add-ons in the same niche that don't require stylesheet knowledge if that puts you off at all.

As for errors, I'll sometimes not completely revise a sentence if I decide to rewrite for tense or aspect, and end up with words missing or in weird grammatical places. And then I'll not see it after three or four checks. Including when coming back to check whether people liked my comment or not.

And then bam, fifth visit, I can't parse what I've written because cabbage there's a wrong word in the middle of a sentence or I've one out entirely. (I did that for effect, but I can't vouch for the previous two paragraphs. Yet.)