Why has facebook come up with untrusted on my pc?

[GemGem]

So I just tried to go to facebook on my pc (My browser is firefox) and its come up with untrusted. I read that going through I understand the risks option and then adding certificate should let me through but it didnt and came up with a blocked domain- contact your network administrator. (I dunno who that is)

I also tried google chrome but its the same thing.

I was able to go to facebook on my ipad okay just not the pc.

I have also tried changing the date and time but it too doesnt work
Under Technical details it has this

facebook.com uses an invalid security certificate.

The certificate is only valid for the following names:
*.opendns.com , opendns.com

(Error code: ssl_error_bad_cert_domain)
Ive downloaded and run cc cleaner and ticked the dns box under system but it still didnt work.

My date and time is correct (16/06/13) and time is correct as well.

[Techno]

If you're SURE the time/date are correct, try clearing your DNS and internet cache* then log in again.

*Use this to clean them safely, make sure DNS cache is checked under cleaner... http://www.piriform.com/ccleaner/ ☺