This appears to be a Firefox issue because this only happens in Firefox. I have 2 Microsoft accounts. I am logged in to my Windows 11 computer with my primary Microsoft account. I can log in to my secondary Microsoft account on Edge (Windows), Chrome (Windows), Safari (on iPhone), but not when using Firefox. I can log in to my primary Microsoft account on Firefox. Both primary and secondary Microsoft accounts require phishing resistant MFA - physical security key, or passkey via authenticator app on mobile phone - of which I have both set up for my secondary account to try to resolve this issue. When I log in to office.com on Firefox using my secondary account I receive a message that says, "We couldn't sign you in. If you're using a passkey from another mobile device, make sure Bluetooth is turned on for both devices." I've got bluetooth turned on for both devices, I've even connected both devices via bluetooth but this doesn't help. I've tried clicking the option to "Other ways to sign in" but it doesn't give me a choice of whether I want to use my security key, or my iPhone passkey. Alternatively on my primary account, I get the option to use my security key, my iPhone device, or even the pin through Windows Hello, and they all work. Again, this failure on my secondary account only happens in Firefox, no other browser has the same behavior. I know I can use Chrome or Edge instead of Firefox, but I prefer Firefox so I want to resolve this. Firefox is up to date 136.0.1 Please help, thanks.