Oddly, I have had no trouble on either of my PCs (home and work) running Windows 8, Firefox, and even noscript (with lotro.com etc. allowed of course).
Yet my freshly wiped Mac (Mountain Lion) with Firefox (and noscript) tells me that the site's certificate is untrusted because "no issuer chain was provided."
On a site I manage, I neglected to install the issuer chain certificate (which is an additional file separate from the standard certificate files) and saw similar behavior. But it's certainly strange that this is only affecting individual computers/browsers. On the site I manage, it only affected Firefox, but it was consistent between Mac and PC (I believe).
I'm not saying anything is wrong on Turbine's end. That would seem unlikely since everything works fine for the vast majority of users. Just trying to throw out another data point in the hopes of eventually helping someone come to a conclusion regarding the root cause of their issue.
P.S. I'd probably have my sys admin check the issuer chain certificate just in case though.
"I went to the trouble and expense of driving my old Honda Civic into a lake to try to prove to you that it won't float. . . only to have you respond: 'Hmmm, interesting. . . would you be willing to drive a Honda Accord into the lake?'"