Firefox is a widely used web browser. However, this doesn't mean you won't face problems while using it. When Firefox seems to be running but isn't responding, it can be quite frustrating. You might want to open it, but it doesn't appear on the screen. How can you resolve this issue? MiniTool Software will provide you with some effective solutions.

Firefox stores your bookmarks, personal settings, and other information in your Firefox profile. For normal operation, it requires an unlocked profile. If the profile is accidentally locked, you may receive a message saying Firefox is already running, but is not responding. In this article, we will demonstrate how to eliminate this error message and return Firefox to its normal state.

What to Do If Firefox Is Already Running?

1. End all Firefox processes in Task Manager
2. Restart your computer
3. Remove the profile lock file
4. Remove the -no-remote startup option
5. Initialize the connection to a file share
6. Check access rights
7. Restore data from a locked profile

Solution 1: End All Firefox Processes in Task Manager

If Firefox wasn't closed properly last time, some Firefox processes may still be running in the background. These running processes are often the cause of the "Firefox is already running" issue. If you see the following interface, you can click the Close Firefox button and then try reopening it to see if it works as expected.

If the above step doesn't work, you can open Task Manager to locate and forcibly terminate these processes.

1. Right-click the taskbar and select Task Manager.
2. Scroll down to find the Firefox process and end them one by one.

Solution 2: Restart Your Computer

You can also simply restart your computer to address the problem. This ensures your computer runs in a clean environment and terminates all hidden Firefox processes. It can also resolve temporary issues that might cause Firefox to not respond, fail to close, or fail to open.

Solution 3: Remove the Profile Lock File

An abnormal shutdown of Firefox leaves lock files behind. To restore normal functionality, navigate to the profile folder and delete the parent.lock file within it.

1. Press Win+R to open Run.
2. Enter %APPDATA%\Mozilla\Firefox\Profiles\.
3. Press Enter to open the profile folder.
4. Locate the folder ending with .default and open it. There should typically be only one folder here, and it should always include a .default folder.
5. Find the parent.lock file and delete it.

Solution 4: Remove the -no-remote Startup Option

Command line options can be used to specify certain startup options for Mozilla applications. However, this can sometimes lead to the issue of Firefox being already running but unresponsive.

If you started Firefox with the -no-remote command line option, you can remove this option and then check if you can open Firefox successfully.

Solution 5: Initialize the Connection to a File Share

If your profile files are stored on a file share, you can access the file share via Windows Explorer beforehand to initialize the connection to a file share.

Solution 6: Check Access Rights

Ensure that Firefox has the necessary privileges to create files in the profile folder. If not, you won't be able to open Firefox as usual.

Here are the steps you should take:

1. Press Win+R to open Run.
2. Enter %APPDATA%\Mozilla\Firefox\Profiles\.
3. Press Enter to open the profile folder.
4. Right-click the .default folder and select Properties.
5. Under General, ensure the Read-only option is unchecked.

Solution 7: Restore Data from a Locked Profile

If none of the previous six methods resolve the issue, you may need to use the Profile Manager to create a new profile and transfer your data from the locked profile to the new one. This post provides useful information: Profile Manager – Create, remove, or switch Firefox profiles.

We hope these methods help you eliminate the "Firefox is already running but is not responding" issue. If you encounter any other problems, feel free to let us know in the comments.

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