In this guide, we'll show you a few different methods for fixing the Firefox is already running but is not responding error message on a Linux system.

First, let's go over a few reasons for why this error may be occurring. It's not uncommon to have an application freeze or "hang" every once in a while, so if this isn't an issue that you repeatedly have with Firefox, you can probably simply kill the process and get back to what you were doing.

On the other hand, the problem has been known to become perpetual in situations where there's an issue with the profile file. Firefox stores a user's personalizations and settings inside a "profile" that is accessed every time Firefox opens. If you're experiencing this error often, it can be helpful to create a brand new profile and import your old settings.

Follow along with our step by step guide below in order to fix this annoying error and get your web browser running smoothly again.

In this tutorial you will learn:
  • How to fix "Firefox is already running but is not responding" error message
  • How to kill Firefox processes
  • How to launch Firefox in safe mode
  • How to remove the profile lock file
  • How to create a new Firefox profile
  • How to reinstall Firefox
Fixing an unresponsive Mozilla Firefox on Linux
Fixing an unresponsive Mozilla Firefox on Linux
Software Requirements and Linux Command Line Conventions
Category Requirements, Conventions or Software Version Used
System Any Linux distro
Software Mozilla Firefox
Other Privileged access to your Linux system as root or via the sudo command.
Conventions # - requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command
$ - requires given linux commands to be executed as a regular non-privileged user

Kill Firefox processes

The first thing you should try to do is simply kill the Firefox process and open it back up. As we stated earlier, sometimes applications will freeze or hang, and this isn't necessarily abnormal if it doesn't happen often.

To kill a process on Linux, you'll need to open a command line terminal on your system. To see the processes associated with Firefox, you could use the following command.

$ ps -x | grep firefox

Rather than killing off these processes one by one, you can use the following kill command to terminate all of them at once.

$ kill $(ps -x | grep firefox | awk '{print }')

If that doesn't work, use the -9 option to force these processes to close.

$ kill -9 $(ps -x | grep firefox | awk '{print }')

Launch Firefox in safe mode

If a browser extension or bad setting is causing problems, launching Firefox in safe mode should allow you to access the application and fix the problem before opening it again normally. Launch Firefox in safe mode from terminal by executing this command.

$ firefox -safe-mode

Remove the profile lock file

If Firefox has shut down abnormally, the profile lock file can be left behind from a previous session and cause errors when starting Firefox again. Try deleting it if it exists. To locate it and determine if it exists on your system, use the find command.

$ find ~ -name "profile.lock"

Then, delete it.

$ rm /home/linuxconfig/.mozilla/firefox/gegouo0x.default-release/profile.lock

Create a new profile

If Firefox still won't start, try creating a new profile in the Profile Manager and launching the application under that profile. We can do this from the command line, as explained in our Firefox and the Linux command line tutorial.

$ firefox -ProfileManager

Then, to launch Firefox under a specific profile, you can use the -P option while specifying the name of the profile. For example, this command would open Firefox with the linuxconfig profile loaded:

$ firefox -P "linuxconfig"

The nuclear option: reinstall Firefox

If you've made it this far into the guide without solving your problem, it's time to consider just reinstalling Firefox altogether. This will clear all existing files, your configuration and settings, and allow you to reinstall a fresh and up to date copy of the web browser.

To reinstall Mozilla Firefox on Ubuntu, Debian, and Linux Mint:

$ sudo apt purge firefox 
$ rm -rf ~/.mozilla
$ sudo apt install firefox

To reinstall Mozilla Firefox on CentOS 8 (and newer), Fedora, and Red Hat:

$ sudo dnf remove firefox
$ rm -rf ~/.mozilla
$ sudo dnf install firefox

To reinstall Mozilla Firefox on on Arch Linux and Manjaro:

$ sudo pacman -R firefox
$ rm -rf ~/.mozilla
$ sudo pacman -S firefox

Conclusion

An application that refuses to open is awfully frustrating, but it's something you have to deal with every once in a while. In this guide, we saw multiple methods for fixing this error in Firefox, from very general remedies to more specific. In the end, if nothing else works, a reinstall is sometimes necessary.

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