Firefox 23.0 canonical 1.0 already running not shutting down or starting up error. States its already running need to shut-down do system restart and close browser.
Go to command line:
Run this command: $ top
you'll see some graphical output, then note the processID (PID) of firefox
- then press 'k' to KILL the process
- you'll be asked to enter the processID (PID) of process you want to kill.
- Just enter the processID of the firefox, and you're ready to go ..!!
And you can use this procedure to kill any process.