Domain Certificate mismatch?

[midwestkc]

So I just got done with my session at Pokerroom, and I go to check my E-mail, and as I'm doing so (in firefox; yahoo e-mail), I get a popup saying that there is a certificate mismatch. What means this? Should I get out my tinfoil hat? I had just checked my progress towards clearing the PR bonus beforehand, so what's the likelihood they have some info that could get them into my account and to my money?

I apologize for such a (probably) stupid question, but I'm not very computer savvy.