dotnina said:That kind of thing happens to me sometimes.
How often is this happening? Try using Expose to leave and then come back to the window. If you didn't try a restart yet, you might consider that too.
It looks like the scrollbar of some window just got "frozen" on your screen -- if that makes any sense. In other words, I suspect it's just a window issue, rather than an issue with Firefox or the site itself.