Funny, strange, weird borders in drupal template (in firefox and not ie)?

Took me forever to figure out that this was due to a tbody style in system.css. This border only showed up in firefox and not in internet explorer. The system style is:

tbody { border-top: 1px solid #ccc;}

I added this to my theme stylesheet:
tbody { border: none;}

Not sure if I'm missing something here, but this worked for me.