[[ -d /etc/pacman.d/hooks ]] || sudo mkdir -p /etc/pacman.d/hooks
cat <</EOF | sudo tee "/etc/pacman.d/hooks/firefox.hook" &>/dev/null
[Trigger]
Operation = Install
Operation = Upgrade
Type = Package
Target = firefox

[Action]
Description = firefox: Remove all the trash...
When = PostTransaction
Exec = /bin/bash -c 'find /usr/lib/firefox/browser/{features,extensions} -name *.xpi -delete'
/EOF

Arch Linux (Manjaro, Antergos, etc). Пару лет, как полет нормальный.