User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0 Build ID: 20171018220049 Steps to reproduce: 1. Enabled U2F security in about:config. 2. Went to GitHub.com and enabled U2F login. 3. Added my security key (U2F Zero) successfully. 4. Logged out of GitHub.com 5. Entered login and password on GitHub.com 6. Got prompt to press security key button. Actual results: USB device icon in Windows 10 kept flashing on and off. Pressing the button on the security key did not log me in. After 30 seconds, GitHub says something went wrong. Expected results: Should have logged me in.

Additional note - FIDO U2F login with the U2F Zero on GitHub works properly, and the Windows 10 USB icon does not flash. Only in Firefox does this problem appear. And only when attempting to login, not when setting up the key.

(In reply to andmib from comment #1) > Additional note - FIDO U2F login with the U2F Zero on GitHub works properly, > and the Windows 10 USB icon does not flash. Only in Firefox does this > problem appear. And only when attempting to login, not when setting up the > key. *on GitHub in Windows Chrome

Using the debugging steps outlined in https://wiki.mozilla.org/Security/CryptoEngineering#Using_U2F_.2F_WebAuthn does not yields any meaningful results. Additionally I'm not able to successfully authenticate in the demo instance of youbi - https://demo.yubico.com/u2f - while the registration is successful the authentication fails silently every time as if the button of the key is not pressed. It works both on github and demo.youbico under Chromium, Win 10.