Mozilla Issue in Python

Hello everybody, i am a python developer and I need some help.
When I try to run firefox with the command
os.system('firefox --marionette -foreground -no-remote -profile "C:\\Users\\utente\\AppData\\Local\\Temp\\rust_mozprofileMzKbdr"')

I get an empty alert error window, with no messages, and after that i cannot use the marionette mode. I need to to this to run selenium test, anyone can help me?