I have reproduced this on OpenSUSE Tumbleweed, with stock Falkon browser (QT+Webkit) and javascript enabled. I have confirmed that this is accomplished through UA sniffing. I reproduce the message in plaintext below:
Sign in with a supported browser To help protect your account, Google doesn’t let you sign in from some browsers. Google might stop sign-ins from browsers that:
Don’t support JavaScript or have Javascript turned off. Have unsecure or unsupported extensions added. Use automation testing frameworks. Are embedded in a different application.