But the bugzilla entry they linked to with that has been unassigned for two years, so maybe they changed their minds or figure the localhost exception is sufficient.
on the developer-edition 69.0b3 it didn´t work - may there are some more flags needed. But on the normal edition 68.0 it worked / it is actually working.
ths helped me (with the 68.0 win edition):
about:config
set the
media.getusermedia.insecure.enabled
from false to true