I'm using FireFox 21.0 and am getting the This Connection is Untrusted message on every https site, including new Google searches. Is there a way to disable this?
If you're just looking to disable HTTPS error pages:
Go to Tools > Options > Advanced "Tab"(?) > Encryption Tab
Click the "Validation" button, and uncheck the checkbox for checking validity. Not recommended, but it should stop them from displaying.
I'd advise making sure your system time is correct, if it isn't, that could be triggering all the certificate errors.
Edit: Yeah, as Tim said, unless you're doing some sort of dev testing, I would NOT disable HTTPS cert errors.
I sit behind a corporate network and had the same problem and "fixed" it by going to [Options] > [Advanced] > [Certificates] > [Validation] and uncheck [Use the Online Certificate Status Protocol (OCSP) to confirm the current validity of certificates]. HTH