ContentTask tasks have a different lifetime than SpecialPowers tasks, with the
former being tied to the lifetime of a message manager and the latter tied to
the lifetime of a window global. That means that existing ContentTask callers
which expect to be able to register load listeners before the creation of a
window global, or which expect to persist after a page has navigated, won't
work as SpecialPowers tasks.
Since those sorts of tasks are not really resilient in the face of Fission,
they should really be written to work differently, but this patch mostly just
reverts them to using ContentTask for the time being.
Differential Revision: https://phabricator.services.mozilla.com/D53744
--HG--
extra : moz-landing-system : lando
