Comment by hotdox

I use next script. It creates temporarily dir for firefox, uses it as a profile dir and remove after firefox closed.

   #!/bin/sh -e
   DIR="${XDG_CACHE_HOME:-$HOME/.cache}"
   mkdir -p -- "$DIR"
   TEMP="$(mktemp -d -- "$DIR/firefox-XXXXXX")"
   trap "rm -rf -- '$TEMP'" INT TERM EXIT
   wget 'https://raw.githubusercontent.com/pyllyukko/user.js/master/user.js' -O "$TEMP/user.js"
   firefox -profile "$TEMP" -no-remote "$@"

It also uses very hardened options from https://github.com/pyllyukko/user.js

It is not my invention, but I lost a link to blog post