Unhelpful answer: it works for me here.
Inside the <iframe>
I see an <html>
inside of which is the normal content.
(This is RC1 under Win2k8.)
Does FireBug show the iframe having any content? Is the iframe being populated dynamically? If so try JavaScript debugging with a breakpoint on the point at which the iframe is populated.
Answering the question in the comment re. the iframe from http://www.htmlcodetutorial.com/frames/_IFRAME.html:
- I see the content document in FireBug
- I do not see it in IE8.
The one thing (compared to an internal example here) is that the iframe you pointed to contains default content... but since this is not shown in IE8's dev tools I can only think this is a defect and should be reported to MS.