hello dmneikirk, ocsp is an advanced security feature in firefox - this error needs to be fixed by the web site in question, so please also contact their support channels and report the issue.

you can temporarily work around the issue and turn off ocsp stapling: enter about:config into the firefox address bar (confirm the info message in case it shows up) & search for the preference named security.ssl.enable_ocsp_stapling. double-click it and change its value to false.
since this will slightly lower your security, it is important however, that after a bit of time when the issue gets resolved by the site (maybe try again in 24 hours), you go back and switch the setting to "true" again!

We are getting exactly the same problem with a site we maintain (https://www.movex.co.uk). This started since updating to Firefox 31.0 on Mac and Windows. As far as we can tell the SSL certificate is properly installed on the server (as validated here http://www.networking4all.com/en/support/tools/site+check/report/?fqdn=www.movex.co.uk&protocol=https). The issue can be worked around client-side by editing the Firefox config as described above, but what do we need to do server-side to fix this issue properly?

hello stv242, your site is loading fine again - maybe your hoster has done some maintenance in the background?

The issue does seem to have resolved itself for our site this morning. Not sure exactly what changed, but for what it's worth we are hosted on Amazon EC2, so perhaps they've updated something.

Thank you for the info. I had done the temporary change to the config based on a blog. That was a good "get around". Fanfiction.net finally responded to the problem about 9 PM EDT. I have reset the config and the website works fine with Firefox again.