Cannot login with Apple ID with Safari. Firefox works fine.

[gctwnl]

I cannot login to Apple services with Safari (latest, Sequoia latest). Works fine with Firefox. Safari either doesn't show anything or presents me with an eternal spinning disc cursor. I am thus typing this in Firefox (I normally use Safari).

I turned off all extensions and restarted Safari, I removed all Apple-related website data and restarted Safari, I tried using a private window, nothing helps.

This is recent. A short while ago I was able to login to all of these fine with Safari.

Is there any known reason for this?

 

[Fishrrman]

Dumb question:
Have you tried shutting the Mac down, and then rebooting?

 

[FreakinEurekan]

Try in Safe Mode. If it's working there but still not after booting back into Standard mode, it's some 3rd party app auto-running.