And just to pre-empt the suggestion, yes, I have upgraded to 6.0.1.

In the last 2-3 days I have been getting "This Connection is Untrusted" screens when trying to navigate to a number of https sites, including Google+, Vanguard, and others. I try to confirm the security certificates and add exceptions, but even after I do that, the sites do not load properly (for instance, no pictures or images).

The problem is not occurring when I use IE on the same computers to navigate to the same sites.

Any ideas as to what's going on and how to fix it?