Apple TV website in desktop web browser - endless login loop

Windows 10. Been watching Apple TV in Microsoft Edge for years with no problems. Today, when I try to log in, I am prompted for my credentials. I enter them, get the two-factor authentication on my phone, enter the code, it's accepted, and then I'm right back to being prompted for my credentials. Rebooted my computer. Cleared cookies and browser history. Nothing works.

Tried Firefox. Confirmed that my installation of Firefox is up to date. Can't watch Foundation because the website says my browser needs to be updated.

Any solutions?