/etc/apparmor.d/abstractions/ubuntu-browsers.d/ubuntu-integration-xul is in apparmor 2.12-4ubuntu5.1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | # vim:syntax=apparmor
# firefox-notify
#include <abstractions/python>
/usr/bin/python2.[4567] ix,
/usr/share/xul-ext/notify/**/download_complete_notify.py ix,
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