Bash check if firefox use internet

Question

I want to check how much internet use Firefox with a shell script.

Here I found good examples to see performances.

#!/bin/sh
free -m | awk 'NR==2{printf "Memory Usage: %s/%sMB (%.2f%%)\n", $3,$2,$3*100/$2 }'
df -h | awk '$NF=="/"{printf "Disk Usage: %d/%dGB (%s)\n", $3,$2,$5}'
top -bn1 | grep load | awk '{printf "CPU Load: %.2f\n", $(NF-2)}' 

might show if it uses the internet or to see a specified application if it uses Intenet?