Safari won't let me sign in to any of my Apple accounts

Hi,

Safari won't let me sign in to any of my Apple accounts, but I can in Firefox.

When I go to icloud.com it doesn't show the Apple ID/password box but it says

"iCloud encountered an error while trying to connect to the server."

When I go to appleid.apple.com it doesn't show the Apple ID/password box just a spinning wheel.

When I tried to sign in here to ask a question, it showed the error message

Safari can't open the page “https://idmsa.apple.com/IDMSWebAuth/signin?appIdKey=891bd3417a7776362562d2197f89480a8547b108fd934911bcbea0110d07f757&path=%2Faccount%2F&rv=1#/welcome” because Safari can't establish a secure connection to the server "idmsa.apple.com".

I've updated to the latest version of Safari and security update. I've also tried zapping PRAM and restarting in Safe Mode.

thanks