For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mimosius:Virtualization/openSUSE_Tumbleweed/home:mimosius:Virtualization.repo
zypper refresh
zypper install firejail
For openSUSE Slowroll run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mimosius:Virtualization/openSUSE_Slowroll/home:mimosius:Virtualization.repo
zypper refresh
zypper install firejail
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:mimosius:Virtualization/15.6/home:mimosius:Virtualization.repo
zypper refresh
zypper install firejail