I don’t think any of this is Firefox specific, OCSP certainly isn’t. Websites have certificates to provide secure connections. But that’s only secure if the certificate is valid. There have been a few different attempts to create a certificate revocation path, so that a company could revoke a certificate if it was compromised for example.

One method was to use the online certificate status protocol, OCSP, but that has a few issues, the new method Firefox is moving to, CRlite, I don’t know much about yet.