RexSystem1 voteoriginally by @Inderix on GitHub OP
On both devices I'm using a Yubikey I attached to my account a little while after account creation.
On firefox I am using the browser based authentication, the whole "insert and touch your security key" thing.
I tested my setup against Yubico's WebAuthn playground as well, and had no issues.
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Comment by @Inderix