Firefox 94 Broke My Hot Keys
Firefox changed the way it attempts to open new tabs in existing windows, from using X11 in version 93 to using dbus in version 94. The firejail profile in 0.9.62, which is the version currently in the Ubuntu Focal 20.04 repositories, block this. This seems to have been fixed in Firejail version 0.9.64. To upgrade Firejail, add the 'deki' PPA, which currently contains version 0.9.66.:
sudo add-apt-repository -y ppa:deki/firejail
sudo apt-get update
sudo apt-get upgrade -y firejail firejail-profiles