Do you now the results testing with IE or Chrome (any version). I have found that the WLC's SSC can have issues at times and may need to be re-generated. I presume you can take you "same machine" and just open the older browser and get to the page, but 15.0.1 firefox will not. Lets assume that; otherwise there could be many other issues.
A packet capture on the client would show the failure problems. I have found that when in this "scenario" IE and Chrome both FIN ACK and end their TLSv1 handshake due to "invalid certificate" or certificate issus. When this happens both Chrome and IE would not get the page, however FireFox always would; it seemed to just "ignore" the problem.
Maybe the new FireFox version is more sensitive. You may need to regenerate your WLC SSC for WebAuth by going to SECURITY > Web Auth > Certificate > "Regenerate Certificate".
You will need to reboot if you do this.
