“1824831 - Can’t sign in with FIDO2 key on office.com”
If this bug report is to be trusted, it looks like Microsoft is blocking FIDO2 hardware keys if you’re trying to use them to log in to office.com with Firefox
... works as a web developer in Hveragerði, Iceland, and writes about the web, digital publishing, and web/product development
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“1824831 - Can’t sign in with FIDO2 key on office.com”
If this bug report is to be trusted, it looks like Microsoft is blocking FIDO2 hardware keys if you’re trying to use them to log in to office.com with Firefox