Authenticator-Prefix by Rajdeep Deb

Authenticator generates two-factor authentication codes in your browser, prefix support added.
Clone of the Authenticator App, but includes prefix support while copying the OTP code. This was built mainly for personal use but then published :)

We were using Sophos VPN which when MFA enabled ask for a password in the format ( passwordOPT ) which is VPN password has to be concatenated with the OTP. A bit weird but it was the only option. This upgrade helps us, and we can have prefix as the vpn password.