The apparmor for Firefox is already installed to
/etc/apparmor.d/but it is not enabled by default.
Step 1 :
sudo apt-get install apparmor-utils
Step 2 :
Make sure the line #120 to #127 are match your language that is installed in your Ubuntu. The line #122 to #123 and #126 to #127 are showing the Traditional Chinese of
Step 3 :
After making the changes (if any), then enable it.
sudo aa-enforce /etc/apparmor.d/usr.bin.firefox
That's all! See you.
Apparmor manual for Ubuntu