Hi Rich,
It is a javascript error, or more precisely, 316 java script errors. The software this forum uses is (poorly) coded in an internet explorer standard. This means that other web browsers will have major problems with it, as the software does not 'play well with others'. Firefox has a few problems, though none are nearly as noticeable as what you're experiencing.
I use Opera, which has different masking and identification options which you can use to make your web browser look like IE to poorly coded websites. However, even with this, up until the latest release of Opera I was experiencing exactly what you are. What I ended up doing was making a cheat sheet of sorts for Opera. I made a list of the smileys and basic BBcode tags and use them as a reference. You can have all the functionality of the javascript editing bar, with none of the heartache.
Update Safari as often as you can, and maybe they will make their code more resilient and better at parsing bad web page coding. I really wouldn't hold your breath for the forum software to get fixed. Also, FYI, its not just FSM, but every forum built on this software framework.
HTH!
Cheers,
Alex