I've tested this on FF 5 and 6 on Windows, and the page renders fine for me. :/
I don't know much about this, but I gather that, to allow for offline storage of you site, you need to add this in your <html> element:
<html class="no-js" lang="en" <font color='"#FF0000"'>manifest="cache.manifest"</font>>
So if you don't put that in, the user won't get the view offline message.