When I open an email in Outlook Express 6 (Windows XP Pro) and try to drag & drop an attachment to the desktop with Firefox 4 open in the background, my computer hangs. This only happens when FF4 is open - I have no problem removing attachments with IE8, Chrome 10, or no browser open. It is repeatable (even after reboot) and it happened with every attachment I tried so far (PDF, JPG, & RTF) I don't have to release the attachment - it's locked up as soon as I start dragging it. The cursor stays a slashed circle even when hovering over the desktop (as opposed to it turning into a box with a "+" when FF4 is not open). When frozen, my CPU is pegged at 100%, which is split between 2 processes - firefox.exe and msimn.exe. I can kill the Firefox application in Task Manager, but it takes awhile (including dumprep.exe after firefox.exe is terminated). The only Add-ons I added was Acrobat X, Flash, and AdBlock Plus. I tried disabling AdBlock, but that had no effect - it still hangs. Any ideas? Can anyone else repeat this on another Windows XP / Outlook Express computer?