Can't save or fill on testdirectly.com

I made an account at https://www.testdirectly.com/patient/security/registration and 1P didn't save the login. Specifically:
Does work:
• Right-click in field > 1P > Save login shows popup, reads name correctly
Doesn't work:
• No dropdown from username/password fields to save login.
• Right-click in field > 1P > Save login popup does not populate URL, username, password, or any other field.

I saved it manually and I have double-checked the data. But when I try to log in at https://www.testdirectly.com/patient/security/login , autofill does not work. Specifically:
Does work:
• When I click the 1P icon in the browser taskbar, my login record is suggested (so I got the domain right).
• Copying from that record and pasting into the form logs me in as expected.
Doesn't work:
• No 1P icon in username/password fields.
• No dropdown from username/password fields.
• Taskbar > 1P icon > login record > Autofill button (either one) doesn't autofill.

Firefox version: 96.0.2

1Password Version: Not Provided
Extension Version: 2.2.2
OS Version: Windows 10 21H2