Sorry for the trouble you’ve all had here. We’ve recently pushed some changes that should have re-enabled the work-around you were using previously. So please do try signing in again as you had done prior to these last few days.
If you continue to encounter issues though, please do let us know!
I am still seeing an issue:
Firefox 66.0.3 (64-bit)
security.webauth.u2f === true
This browser doesn’t support the FIDO U2F standard yet. We recommend updating to the latest Google Chrome to start using security key devices.