I realize I'm just one person, but the dealbreaker for me is still the very minimal WebAuthn support. No soft tokens, and therefore no TouchID/Hello support.
The difference in friction between "Getting my Yubikey out of my bag" and "Pressing the TouchID button" is enough to keep me on Chrome.
I don’t know about TouchID support, but Windows Hello has been supported by Firefox for at least a couple of years or longer now.
I use fingerprint authentication on a laptop with Windows 10 and Firefox on sites that allow me to use this as the second factor.
There is also a flag in about:config (signon.management.page.os-auth.enabled = true) to make sure this support is enabled.
Initially I found that it wasn’t working, and then I went through troubleshooting mode (disable all extensions) and found an extension that was blocking this from working (I didn’t spend time on investigating why or if someone else had seen the same issue).
That's for signing in to Firefox (as well as unlocking the built-in password store, I believe). I'm referring to using TouchID for WebAuthn (i.e. "a built-in Yubikey")
The difference in friction between "Getting my Yubikey out of my bag" and "Pressing the TouchID button" is enough to keep me on Chrome.