There is a kerfuffel about Adobe Java Plugins and malware currently. Plugins are being disabled. This may be part of the problem.
Google News and many other sources have reports on the situation. Even the FBI has weighed in.
@Annie - "Firefox says "plug-in blocked", Safari shows a blank window, and Internet Explorer says..."
How did you tell FM to use each of the browser applications as its web viewer, please?
I just point a browser to my website, which is a database using FileMaker's Instant Web Publishing webviewer.
Ah, thank you! I thought you had found a way of changing the browser 'engine' that Filemaker used when displaying a webviewer.