Wow, the bolding doesn't show at all in your case! It reads just fine on Safari. But it's not a very common font, maybe that could be (at least part of) the reason it acts differently on different browsers? It's not a particularly web-friendly font, compared to for instance Helvetica or Trebuchet MS.
While I'm perfectly able to read the text on the forum as it is, I've noticed that I more and more often leave a thread that I'm actually interested in reading and participating in, just because my eyes get tired very quickly. And zooming in shouldn't feel like a huge inconvenience, but it does when I never have to do it elsewhere, so I never bother, I just leave the forum instead :/
But again - simply increasing the size would be very helpful.