I raised the same issue back in June (http://forum.aws.chdev.org/t/pdf-compliance-issue-inc-rendering-in-firefox/109).
Whatever Firefox uses to render PDFs is unable to deal with the corrupt xref. A message was added to beta search results warning about using Firefox. I just had a look and the documents I had issues with seem to be rendering in Firefox now (although the warning message is still there).
So I don’t know if they fixed something or Firefox updated their ability to render corrupt PDFs. If your still encountering issues with this it might indicate the latter?
When I encountered the problem it was all electronically filed documents that were effected.