Comment # 1 on bug 1094767 from Olaf Hering

Do this, and try again:

zypper ar -cf \
  http://download.opensuse.org/repositories/home:/olh/openSUSE_15.0 \
  olh
zypper mr -p 123 olh
zypper ref -r olh
zypper in --allow-vendor-change -r olh MozillaFirefox