You're missing the point. Brown is not apologizing for Britain having behaved *illegally*, or for having prosecuted Turing. The law was applied as written at the time (I'm assuming; I haven't checked). He's apologizing for Britain's treatment of Turing, period. The law was unjust, and the results horrific. Britain is recognizing this and doing the only thing it can at this point: express its regret.
The problem is that CapitalOne's web server does not supply the certificate for the intermediate CA which issued the server's cert, so Firefox can't make a chain back to the root (which it does have). The reason it works in some other browsers, is that the web server cert itself contains a pointer to the needed certificate embedded in it; the browsers in which it works fetch the intermediate cert from there; Firefox simply doesn't do that. It actually works in the latest release of Firefox, as well.