Mozilla firefox and 'about:blank'!

Well, last week Internet Explorer(IE) on our laptop was hijacked by 'about:blank' - spyware/adware. It had earlier too and I had managed to fix it using Ad-aware 6.0 and Spybot . But this time the damn thing is now, taking its revenge. It is NOT going. So out of frustration I decided to change my browser to Firefox.

And ,life has been a lot more easier now. I am still finding my way around it though. It is GOOD.
So anyone having trouble with IE ,try Firefox. But the damn 'about:blank' still pops up when I go onto Yahoo Messenger. Does anyone have any suggestions?