Am seeing an issue with Firefox 9.0.1 (so far in Mac only) in which if there's content in a nested iframe of the kind:
Main file:
<iframe src="testFF1.html" width=600 height=800>
</iframe>
testFF1.html:
<iframe width="560" height="315" src="http://www.youtube.com/embed/DAl5nv7tIR4" frameborder="0" allowfullscreen></iframe>
So far am unable to show a different video on the second iframe, it always shows the same one, no matter which address I use.
You can see the issue here:
http://crashdummy.meetai.com/testFF.html
If I edit the second file (testFF1.html), i.e. to display another video, I have to restart FF in order to see the change.