@eeji, I visited your forum with the latest version of Firefox (3.6 as of now) and I didn't have any issues.
HardStyle wrote:What version of firefox are you using?
Do you still have the problem if you use a fresh version of prosilver_se ?
However, I still have this issue on http://www.startrekguide.com/
(hope this isn't considered spam, as it is related to the problem).
I viewed STG in IE7, Safari 4.0.4, Chrome 4.0 and Opera 10.10 and I didn't have any problems with the layout of the forum descriptions.
I'm not sure what version of phpBB STG is running, but I could ask if you want.
EDIT: I checked again on STG and there was no problem.
EDIT (again): It seems to be an issue with the page loading. If you refresh the page the problem should disappear. This is most likely a bug in Mozilla.