I cannot sign into Discover Card when I use FireFox. I talked to Discover Card about it. They say the most frequent reason it happens is because Discover Card is not on your safe list. I tried signing in on my other PCs with a Ubuntu OS and their browser Opera works fine on signing me in. Within the last two weeks I installed Mint on two of my PCs. works great except for not being able to sign in to Discover Card. I am not having that problem on any other sites. I doubt if my cache is full as my usage being new OS has been minimal. I just tried signiing in with this PC after installing Mint yesterday. I get the same message "We're sorry. Your request cannot be completed at this time. We sincerely apologize for this inconvenience and are working to resolve this issue soon." Discover wants to blame Firefox. Personally I think It has to do within the Mozilla VPN. I say that because I often had the same problem when I used McAfee's VPN. Discover maintains it has nothing to do with VPNs and it is a trust issue. Eventually I want to replace Ubuntu with Mint. But I cannot until this problem is fixed. Opera is also running a VPN when I sign in so this would support Discover Cards theory about Firefox not having Discover on a safe list. I think they have it wrong though. If your site is blocked you are not on Discover's safe list. I wish we could get a meeting of the two minds instead of me trapped in the middle. Hope this helps.