U2F/Yubikey support in Opera 38+
Currently, this functionality is only supported in one of the major browsers – Chrome. Bringing this functionality to Opera would reduce user dependence on software-based TOTP applications like Google Authenticator, which are available on smartphone OSes and not always the best 2FA method.
A FIDO U2F device can be registered and used with online services as a second factor for authentication.
Current (actual) behaviour
Upon trying to register a Yubikey as a second factor for a Google account, a message pops up stating "Extension not installed." The registration process is interrupted.
Other background information and resources
Multiple online outlets, including a FAQ page on Yubico's website, mention that only Chrome supports Yubikey as of this writing.
Hi @julesmazur, this feature seems to be implemented ("DNA-42872 Implement FIDO U2F" - the change log) in the latest Opera developer. If you want to check it out, you can enable it as follows: after you install the developer version, go to the address bar, paste
opera:flags#cryptotoken, and press Enter, select "Enabled" from the drop-down, and press "Relaunch Now".