Sometimes I have part of the text running off the right side when I preview a post and can't read the whole thing with FF. There have been a few times when reading posts, part of the text is off the right side and I couldn't scroll to get it onscreen. I think those times I had enlarged things more than usual (CTRL +) to read more easily. Considering all the variables they're dealing with, different browsers and operating systems, I'm amazed there aren't more issues.
I should never overestimate my basic arithmetic skills.