Code review comment for lp://qastaging/~henn/firefox/fix-for-1665535

This access should be added to /etc/apparmor.d/abstractions/ubuntu-browsers.d/multimedia instead. The firefox profile edited here is meant to be minimal, with abstractions from /etc/apaprmor.d/abstractions/ubuntu-browsers.d/ used via /etc/apaprmor.d/abstractions/ubuntu-browsers.d/firefox. By default, /etc/apaprmor.d/abstractions/ubuntu-browsers.d/firefox will include multimedia.