Seeing this image right now.
Background info from Firefox Troubleshooting Information:
Build ID 2019022821563
OS Linux 5.0.2-arch1-1-ARCH
I cannot register any keys with Firefox 66.0.3. `u2f` is enabled in `about:config` and it definitely works on other sites. Github seems to only support Chrome for registering keys for some reason.
As others have reported, this is not actually resolved. Firefox 67 just released as stable, which has u2f enabled as a default. I'm still seeing the message even after successfully using u2f on other sites:
- Firefox 67.0 (64-bit) fedora - 1.0
- Fedora 29 x64
This is not resolved.
Right now if I get a login prompt from GitHub while I'm using Firefox, it asks me to enter my password. If I change my user agent to Chrome, still using Firefox, it properly adds that I can press a button on my security key to log in.
So U2F is still being blocked in Firefox based purely on user agent.
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!
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I still can't register my Yubikey through Firefox, there is this message on the security page : "This browser doesn’t support the FIDO U2F standard yet. We recommend updating to the latest Google Chrome to start using security key devices. ".
I succesfully registered and use my Yubikey as U2F through this browser on other providers (AWS, ...).