When OSCP querying is disabled (i.e. security.OCSP.enabled=0) then FF doesn't show the typical "green bars" from EV certificates. Since FF's use of OSCP is however completely pointless as it's not enforced (security.OCSP.require defaults to false) it seems pretty pointless to not show the EV green bar in that case - after all it's still an EV cert, just without the anyway useless check for revocation.
I can reproduce this case. I see the "This website does not supply ownership information." in Page Info dialog while OCSP is disabled. Maybe related to Bug 585122.
In the case of EV, if Firefox can't (or has been configured not to) obtain recent revocation information, it doesn't display the green EV indicator. This is expected behavior.