I recommend everyone to use a YubiKey as a second factor authentication method for increased security. After a fresh installation of Pop_OS!, the YubiKey authentication in Firefox doesn’t seem to work (I assume the same holds true for Ubuntu and its other derivatives like Linux Mint). The solution is easy: With a simple sudo apt update && sudo apt install libu2f-udev, the necessary U2F libraries are installed and the YubiKey will start to work. Stay safe on the Internet, everyone!