How To Fix “Firefox is running but not responding” Error

If you are a Firefox user, you must have seen the above pop-up more than once. A lot of people get confused as to what to do next and end up restarting their computer. Well, lucky for you we are here to tell you how to resolve this error so that next time it happens, you are prepared.

But first, let’s understand why this happens- There can be two reasons why you are seeing this error

  • Firefox profile is where all your bookmarks, personal settings, and other information is stored, if this profile gets locked, Firefox will show the above error as it needs an unlocked profile to startup
  • Or if Firefox didn’t close properly: It must be frozen or in the process of closing

What can I do about it?

Close Firefox and Wait Few Seconds:

The first thing you can do is just simply click “Close Firefox” on the above pop-up. As we mentioned, it must be in the process of closing down. This usually happens if you have closed all the Firefox tabs quickly and opened a new one immediately. Firefox may be still saving the data before quitting therefore sometimes if you wait a few seconds the problem will be resolved. However, if the above thing doesn’t work out, don’t be sad. There is still a way to resolve this error

Go to Task Manager

Another way to get rid of the pop-up is by going to Task Manager. Here’s how to do it. Press Right-click on your taskbar then go to “Task Manager” or if you are into keyboard shortcuts, press Ctrl+Shift+Escape

The first option that you will see is “Application” however since Firefox is running in the background and it’s invisible, you won’t see it here. No worries! Go to “Processes”, just next to Application.

Here you can see “Firefox.exe”, click this entry and then click “End Process” below. Click “Yes” on the warning dialogue box.

There can be more than one “firefox.exe” entries, if present, repeat the above process for each of them and then close Task Manager Windows. 

Check access Rights

Sometimes the error can occur, if the profile from a file system doesn’t have the proper permission. In this case, for example, if the file is mounted with Read-Only permission.

How to check if the allowed permission is appropriate? 

Go to the main Firefox profile folder, then right-click on it. Once you see “Properties”, click on it. And then go to “General”


By now, you should see something like the above picture. In “Attributes” you can see two options: Read-only and Hidden. Make sure “Read-only” is not ticked. If it is marked, click on it to deselect it and then press “OK”.

Unlock Profile in Firefox

If you tried the above method and there is still no success, the most likely cause is that your profile is locked. All browsers, including Firefox, lock personal profile files when it is used. This setup also makes sure that only a single copy of Firefox is working on a profile at one given time. This lock is removed when we close the tabs. In a case, where Firefox is abruptly closed, this lock might stay on and since Firefox can’t open a locked profile, “Firefox is already running” error might appear.

Worried about how to solve this? Don’t be! There is a solution to this. To unlock your profile, you need to delete the locked files by yourself. However, the most important thing before doing this step, is to make sure that Firefox is closed (not even running in the background) therefore you have to close it from Task manager first before doing this step, or else there is a chance that your profile might get corrupt.

Once you closed Firefox (from task manager too), you are ready for the next step. Now go ahead and press Windows Key+R

Once you see the above box, copy this link %appdata%\Mozilla\Firefox\Profiles

And paste it in the blank space next to “Open”

Then click “OK” 


You should now see a random file in “Profiles” ending with default. These files may start a weird combination of numbers and words but end usually on default. Double click on this file. After this, you will see a list of files, press P and search for “parent.lock”

FireFox Error delete parent lock

Once you locate “parent.lock”, select it and right-click on it. Go down and press “Delete”. Firefox should run normally now.

Restart Your Computer

If all the above fails, then you might as well try the most common method used whenever there is even a slight problem. Yes, go ahead and restart your computer. Restarting pc after doing all the above should start Firefox.

The above-mentioned methods have solved the issues of the majority of people. Hopefully one of them will be effective for you too.

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