This is a problem with the web site generally, not the game itself.
When you hover over the main navigation (Home|Account|Profile|Skills|etc) in Safari, as the fade-in highlight effect triggers, the rest of the text on the page briefly flickers. The forum topic lists are the worst example - on these pages the body of the page blanks completely for a fraction of a second. The effect is vaguely disconcerting.
This only happens for me in Safari. Firefox and Chrome are fine. I tried disabling extensions, but the problem remains.
Safari 5.0.3, OS X 10.6.6