Did your Firefox browser become unresponsive and it won't close or reboot?

On Ubuntu, you can force quit the Firefox application by using the pkill command in your terminal.

If you don't already have a terminal window open, you can open one with the CTRL+ALT+T keyboard shortcut.

Then, execute this command in your terminal to kill all processes running the Firefox browser on your machine:

    
      sudo pkill -9 firefox
    
  

This command runs the pkill command with the -9 option, which is the SIGTERM signals used to tell a process to terminate.

After successfully running that command, all the instances of Firefox running on your machine should now be closed and terminated.

If you don't want to kill all the Firefox processes running on your machine, you can also kill individual processes. To do this, you need to first list out all the PIDs (Process Identifiers) running Firefox and then use the sudo kill -9 PID command to kill that specific process.

You can list all the processes running the Firefox browser with this command:

    
      ps aux | grep firefox
    
  

The command uses ps aux to get all the processes running on your machine and then grep firefox to filter out everything but processes running Firefox.

This will output something that looks like the following:

    
      nick     32215 13.1  1.9 2998852 322092 ?      Sl   22:20   0:05 /home/nick/firefox/firefox ...
    
  

The first number you see in the output after the username (32215 in the example output above) is the PID for that specific process.

You can also modify the output to only show the PID numbers:

    
      ps aux | grep firefox | awk '{ print $2 }'
    
  

This output will look like this:

    
      32215
      32686
      35696
    
  

Now that you have the PID/s for the process running Firefox, you can end it with this command:

    
      sudo kill -9 PID
    
  

That will kill only the specific PID number you give to the command.

Thanks for reading!