TL;DR
zypper install u2f-host
More details
This week openSUSE Leap 15.2 came out and I dared a fresh install on my workstation - before running Tumbleweed and causing my too many updates to install for a machine that gets fired up only 1-2 times per week. It always runs smoothly, but I don’t need to be cutting edge on this machine. Here I prefer stability and less maintenance.
Turns out, the Yubikey doesn’t work out of the box with Firefox on a Desktop installation with Mate as default desktop environment. No worries, you only need to install u2f-host and restart Firefox, then you’re good to go :-)
zypper install u2f-host
Leap 15.2 is awesome - A refreshed 5.3 Kernel that runs smooth and gives a rock-stable environment. I find this a perfect fit for my workstation, where I do occasional photo editing, some coding and compiling (if I still do it locally) alongside occasionally firing up Steam as well :-)