I'm running 10.04.
The firefox profile was already present. It's part of the firefox package. That's an old thread, so maybe it wasn't the case at that time.
To enable the firefox profile, I had to remove this symlink:
That was the only profile that was disabled in that manner.
sudo rm /etc/apparmor.d/disable/usr.bin.firefox
Then I (re-)loaded the profile:
My understanding is that any profile in /etc/apparmor.d/ is automatically loaded when the apparmor service starts. If you add or change a profile, the change will only take effect when that profile is explicitly reloaded or when apparmor is restarted.
sudo apparmor_parser -r /etc/apparmor.d/usr.bin.firefox
A profile in /etc/apparmor.d/ can be disabled by placing a symbolic link to it in /etc/apparmor.d/disable/.
This shows which profiles are loaded, and whether they're in complain-mode or enforce-mode:
sudo service apparmor status