There are two basic ways to revoke a certificate - one is to black list it in client software, and the other is to publish it on a certificate revocation list server. What Mozilla is doing is the former.
The advantage of doing it in the client software is that no one can block it unless they can compromise the software itself. The disadvantage is that it takes a software update or upgrade to become effective.
On the other hand, the CRL server or distribution point is generally operated by the corresponding CA, so if you don't trust the CA you have no alternative than to remove it from your trust list.