www/firefox: attempt to fix mic on pulseaudio

careful testing revealed that the microphone worked "sometimes",
with the "not working" state manifesting as follows: pulseaudio sees
a signal from the microphone but firefox (and it's components) fails
to show up on pulseaudio's source-outputs and firefox gets no audio
signal.
Applying the patch from upstream 1735905 seems to improve matters
greatly.

PR: 257639
Reported by: many
Obtained from: https://bugzilla.mozilla.org/show_bug.cgi?id=1735905

(cherry picked from commit 2af447c8bac175a02de64aad1e36ad849df2f57f)