As I'm trying to migrate to Linux #snapcraft packages (strict confinement -> sandbox -> more security) I noticed my #u2f keys didn't work in #firefox from snap. This is because U2F is not by default "plugged" into the snap, but that's an easy fix:

sudo snap connect firefox:u2f-devices

Full thread here https://forum.snapcraft.io/t/u2f-not-working-in-firefox-snap/14039