Sometimes programs tell me I can't start it because there is already another instance of it running. Best example would be Firefox and Chromium, but this problem accounts for many applications.

I cannot find the applications PID in the running processes.

How to kill all running instances of a program, e.g. Firefox?

I tried:

ps ax | grep firefox

But everything I can find is:

8193 ?        Rl     0:08 /usr/lib/firefox/firefox

I tried:

kill 8193

But I get:

Process not found

Actually, even when Firefox is running accurately, I cannot find its instances in ps.

What did I miss?