I had this problem about a month ago, until an update fixed it. But the last two updates brought it back again. The attached screenshots probably describe it better than I can. It seems to occur most when viewing pictures on websites. (All perfectly respectable, I hasten to add!) I have a feeling that it may be related to Flash, and as a matter of fact, I've also had problems with Adobe reader, which is why I've resorted to a plug-in. As an aside, the "send report to Firefox" invariably fails, but the reload works. I've removed and reinstalled Firefox today, but it hasn't helped. I'll be grateful for any advice, thanks.