Fix: Firefox Is Already Running but Is Not Responding

It’s not uncommon to have a browser(or any application for that matter) stop working or freeze sometimes. Every once in a while, a simple application restart should suffice to load all your tabs. But, if the issue is more persistent, you need to do something else other than a reset.

Firefox is known to have this issue for a long time and across all browser versions. The message means that it found Firefox already running and is refusing to open it a second time. But, if it is already running, shouldn’t you be able to open it? To understand this, let’s investigate why the message pops up.

Why Do I Get This Message?

This means that a different instance of firefox is running in the background. But you may also get this message if firefox crashes while in the middle of something. It is also possible that Firefox updated and some changes didn’t take place. If this happens then firefox isn’t going to shut down by itself like it normally does.

There are a couple of tasks that firefox does when exiting. Firefox may freeze due to application bugs and become unable to complete those tasks. Due to this, the system may falsely detect a different firefox running in the background. To understand how we can fix this issue, first, we need to understand what a Firefox Profile is.

What is Firefox Profile?

Firefox Profile stores all the changes that you stored in Firefox. It is a folder in your local storage disk separate from the main Firefox program data. This is particularly helpful when anything goes wrong in your Firefox. You can reinstall the application without losing any of your settings.

For consistency reasons, the browser locks a profile folder when it starts up. If a profile is already locked, it means that the browser application has created a lock file. This lets the system know that the application is using that profile to run. 

As mentioned above, it’s going to remove that lock file when it shuts itself down. If it failed to do so, the error message appears the next time you open the browser.

Firefox Not Responding, Firefox Is Already Running but Is Not Responding(Fixes)

Kill Off the Running Process

For Windows

1. Right-click on the Start Menu and open Task Manager.
2. Expand to get a detailed list of processes.
3. Scroll to check for any firefox.exe processes and select them.
4. Click on End task to terminate the process.
5. Repeat for each extra instance of the process.

For Linux/macOS

1. Open Terminal.
2. Type in : Ps -ef | grep firefox
   Get a list of all running processes and display the ones containing the word firefox.
3. Locate the PID as shown in the screenshot(18778,18985,19013 etc.).
4. Kill -9 18778
   Stops the running process as specified by PID.
5. Repeat Step 4 for each instance of running firefox. Alternatively, you can just type all PIDs in one line separated by a space.

Remove Lock File on Profile

For Windows

1. Press Win + R together to open the Run window.
2. Type %APPDATA%\Mozilla\Firefox\Profiles\.
3. Hit Enter to bring up a folder of existing profiles.
4. Open the .default folder.
5. Look for the parent.lock file inside this folder and select it.
6. Press the Del key or right-click on it and select delete to remove this file.
7. If you have set up more profiles, go inside each folder and repeat the same steps.

For Linux/macOS

1. Type Find ~ -name lock
   Find the path of the lock file if it exists.
2. Rm -f /home/sndp/.mozilla/firefox/bqyvkgc4.default/lock
   Delete the lock file by providing its full path.
   Note: Try again using sudo if you get permission denied.

Run Under Safe Mode

For Windows

1. Open Powershell.
2. Locate the installation location of firefox. Generally, it’s C:\Program Files\Mozilla Firefox\firefox.exe as default.
3. Assuming default location, Type & ‘C:\Program Files\Mozilla Firefox\firefox.exe’ -safe-mode. Press Enter to open Firefox under safe mode.

For Linux/macOS

1. Open terminal.
2. Enter Firefox --safe-mode
   Launches firefox after specifying the safe mode argument.

Create a New Profile

For Windows

1. Open Powershell.
2. Assuming default location, Type  & ‘C:\Program Files\Mozilla Firefox\firefox.exe’ -ProfileManager. Press Enter to open firefox’s choose profile window.
3. Click on Create Profile button to bring up the profile wizard.
4. Click Next.
5. Enter the new Profile name and select Finish.
6. A new profile now appears in the list.
7. Check the checkbox as shown to load the new profile automatically at startup.
8. Click Start Firefox.

For Linux/macOS

1. Open terminal.
2. Type Firefox -ProfileManager
   Opens the profile manager dialog for firefox.
3. Click on Create Profile button to bring up the profile wizard. 
4. Click Next.
5. Enter a profile name and click Finish.
6. A new profile now appears in the list.
7. Check the checkbox as shown to load a new profile instead of old ones.
8. Click Start Firefox.

Check Folder Access Rights

For Windows

1. Press Win + R together to open the Run window.
2. Type %APPDATA%\Mozilla\Firefox\Profiles\.
3. Hit Enter to bring up a folder of existing profiles. If you have only one, it’s named default.
4. Right-click on the profile folder and select Properties.
5. Under the General tab, make sure the Attribute “Read-only” is off. We want this directory to be writable.
6. If not, then uncheck it and hit Apply and OK.

For Linux/macOS

1. Open Terminal.
2. Type in : Find ~ -name lock
   Find the path of the lock file if it exists.
   We are doing this to get the location of the lock file which is used in further steps below.
3. Ls -l /home/sndp/.mozilla/firefox/bqyvkgc4.default/lock
   Display a long list format of information of the lock file.
4. Make sure that the owner and group are the same users as the regular user as shown below. Use Step 6 to restore ownership.
5. Chmod u=rwx,g=rwx,o=rwx /home/sndp/.mozilla/firefox/bqyvkgc4.default/lock
   Restore correct permissions to the file.
6. Chown sndp /home/sndp/.mozilla/firefox/bqyvkgc4.default/lock
   Restore correct file ownership. Replace sndp with your username.

Reinstall Firefox

For Windows

1. Go to Start Menu and search for Add or Remove Programs. Press Enter.
2. Under Apps & Features, search for Firefox under the list of installed programs.
3. Select Firefox and click on Uninstall.
4. Restart PC after Windows completes the process.
5. Download the latest version of Firefox and install it.

For Ubuntu/Ubuntu-based/Debian-based

1. Open Terminal.
2. Enter Sudo apt purge firefox
   Completely remove firefox from the system.
3. Rm -rf ~/.mozilla
   Remove config files associated with firefox.
4. Sudo apt install firefox
   Reinstall a fresh version.

For CentOS/Fedora/Redhat-based

1. Open Terminal.
2. Type Sudo dnf remove firefox
   Completely remove firefox from the system.
3. Rm -rf ~/.mozilla
   Remove config files associated with firefox.
4. Sudo dnf install firefox
   Reinstall a fresh version.

For macOS

1. Open Applications folder.
2. Right-click on Firefox.
3. Select Move to Trash.
4. Open Finder.
5. Go to Library.
6. Select Application Support.
7. Right-click on Firefox.
8. Select Move to Trash.
9. Select Empty Trash to remove from the system.
10. Download the latest version of Firefox and install it.

Frequently Asked Questions

Close Firefox Button on the Error Message Doesn’t Work?

If the close Firefox button does not work, you may need to end up force-killing it. Firefox provides an option to force quit the application in case of emergency cases. First, try the following methods to quit firefox.

1. Press Ctrl + Q together. If running on a macOS, press Command + Q instead.
2. Click on Hamburger menu and select Quit.
3. Close each tab one by one and attempt to close.
4. If none of these work, do the following to force quit.
   • In Windows, Open Task Manager. Select Firefox and click on End Task.
   • In macOS, click on the Apple menu and select Force Quit.

One thing to note here is that you should not force quit unless absolutely necessary. Force quitting multiple times can create duplicate session profiles which will give you trouble when trying to reopen it. If you cannot open firefox after closing it, follow the steps above to fix the issue.

How Do I Run Two Firefox Profiles at the Same Time?

You can run two firefox profiles at the same time using Firefox Profile Manager. To open firefox profile manager before running firefox, try the following.

In Windows,

• Open Powershell.
• Assuming default location, Type  & ‘C:\Program Files\Mozilla Firefox\firefox.exe’ -ProfileManager press Enter.

In Linux and macOS,

• Open Terminal.
• Type Firefox -ProfileManager  and press Enter.

Continue below for all platforms.

• If you see just one profile, you need to create a new one. Refer to the create a new profile section above.
• Once created, click on Start Firefox.
• Repeat the above step to open the profile manager a second time.
• Select a different profile and click on Start Firefox.

Does Running Multiple Profiles on Firefox Cause Firefox Not Responding?

Running multiple profiles is a feature provided by firefox. For a majority of users, multiple profiles work just as fine as using a single profile.

That being said, an average internet user may not know how to set up multiple profiles. The steps may be confusing to setup and access. Thus a less experienced user is more likely to get stuck due to profile locks, deleted default profiles and so on.

Thus you are likely to run into the firefox not responding issues if you haven’t set up profiles properly.

Multiple profiles are generally used by developers and more advanced users. If you are comfortable using multiple profiles and can troubleshoot when needed, it actually serves you a lot. Personal information such as bookmarks and passwords are stored in profiles.

If you use a shared PC, you may want to take advantage of this feature. But make sure other users are also comfortable using it.