When I opened up an e-mail in Netscape mail with attached files, in this case .c files for a homework assignment, clicking on a file for download caused the screen to black out, and come back, as if it were trying to change resolution but failed. I am using an AMD k6-III, MS Intellimouse Explorer (attached via PS/2), and a ATI Xpert 98 PCI video card.
As unlikely as this bug report seems, I've seen it also. Very weird.
This is not something we can fix, unfortunately; it's something intrinsically wrong with the netscape binary itself. You can try reporting it to netscape at: http://help.netscape.com/forms/bug-client.html