Like others, I get this message when using the back button on Firefox with ATP:
"Document Expired
This document is no longer available.
The requested document is not available in Firefox's cache. As a security precaution, Firefox does not automatically re-request sensitive documents.
Click Try Again to re-request the document from the website."
I don't get this with Safari on iPad, though.
Another thing I've noticed is that "New" doesn't go away when I've read a thread but I think that depends on how I back-track. Eventually it does, but until then I have to try and remember what I read.
Edit: Forgot to add that ATP is not at all slow for me, and I don't have the fastest internet. It is optimistically called "high speed", which is up to (that being the operative term) 3mbps.