Well, here the lines don't break! I thinks it's a Firefox problem and not WP-related, but still... shouldn't it be possible that WP takes care of this?
I'll try to illustrate my point with an example. I stole this text from the dev blog:
Plus, because of the archiving style built-into Mo-va-ble-Type the site was swelling up in size with web files all over the place. I’m not a fan of sta-ti-cally created pa-ges at all. I think it leads to bloating and to make changes, you have to re-build every single one of them pages. So, I have been looking for an-other blogging tool to run this site off of. I looked at all of the major players other than MT and found Word-Press to be the best out of all of them. I check-ed it out and even created a test in-stall with some of my existing en-tries.
I placed hyphens in every (long) word. WP should be able to recognize them and break the words at the end of a line. And, of course, drop the other hyphens in that word (or it becomes a mess).