Murphy's Law rules the day today, sometimes there's just no getting around it *grin*.
We have been doing extensive work on the forums over the last few weeks and it appears that you are experiencing a bug that showed up recently, but had never been seen before. A few random users (and unfortunately it only applies to newer users) are experiencing the missing Post and Reply buttons. As the issue is reported I am able to correct them on a per user basis (we know what the problem is), but we should have a broad fix for this in place within the next 24 hours. Please bear in mind that this is not a general problem, it only affects high-volume / high-traffic instances of the forum. Since we've not yet released this version, no other sites are affected... we eat our own dog-food here which usually results in better software, but sometimes puts us on the bleeding edge of problems like this.
The FF issue you are reporting I can only assume is the one I experienced yesterday (though only for a moment)... the menu rendered as a list for me instead of drop-downs. The issue has been reported and appears to be tied to a rare caching anomaly that the engineers are looking at how to prevent. I personally use IE, FF, Chrome, Opera and Safari and noted that it only manifested in FF (and again, only briefly).
Ironically, your feedback is very much appreciated because it is only with feedback that we are able to respond. Whether you opt to use DotNetNuke in the future or not, I appreciate that your participation will actually help to improve the product for others.
Cheers