[ Fixed ] Firefox Not Responding | Firefox Already Running | Firefox Cannot Restart Due To Profile In Use | Close Firefox Window Appearing | Firefox Already Running

by Rohit Khurana on August 14, 2009



This problem is regarding a frequent error I face these days in my computer after I upgraded to firefox 3.5. Every time when I close firefox by closing all its windows and the next time I try to start firefox the following error message box appears


If you can’t read the error message, here is the error message

Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system.

This message may appear due to following known reasons like

Trouble Cause #1 – Firefox Profile Lock Not Released

The first foremost reason behind this error is when firefox is not closed down properly due to which firefox profile lock may not get released


Fix Cause #1:

In this case firefox creates a lock on the profile getting used in firefox, but sometimes due to improper shutdown of firefox application the lock may not get released which cause the above error message to appear. In that case you will need to delete the following file from the profile folder depending on the operating system you are running.


Open the firefox profile folder and delete the following file,

  • "parent.lock" in Windows,
  • "lock" and ".parentlock" in Linux
  • ".parentlock" in Mac OS X

The profile folder exists at following in different operating system, some of these folders may be hidden.

Operating system Profile folder location(s)
Windows NT (NT 4.x, 2000, XP, and Vista) "%APPDATA%\Mozilla\"
Windows 95 (without Desktop Update) C:\Windows\Mozilla
Windows 95 (with Desktop Update)/98/Me C:\Windows\Application Data\Mozilla\

C:\Windows\Profiles\<Windows login/user name>\Application Data\Mozilla\

Unix/Linux ~/.mozilla/
Mac OS X ~/Library/Mozilla/

~/Library/Application Support/

In order to open profile folder for windows users

Press [Windows Key]+[R] >> Type in %APPDATA% >> click OK


Note: When you try to delete the "parent.lock" file and you receive the error, "Cannot delete parent: The file or directory is corrupted and unreadable", restart the computer and run the error-checking tool Chkdsk Windows 2000, XP, Vista and 7 or ScanDisk in Windows 98, ME.



Trouble Cause #2 – Firefox 3 Delayed Shutdown 

This error can also occur due to delayed shutdown in firefox 3 or above due to heavy usage of Firefox or too much history remembered in some heavy profile of firefox which makes it slow and cause delayed shutdown so when you close firefox window and try to re open it too soon after it was closed you will see this error.

Fix Cause #2 – Just wait for 2-3 minutes after closing firefox to re open it again


Trouble Cause #3 – Firefox Cannot Find the Profile Folder

In this case Mozilla firefox may not be able to find the profile folder then it will report this error message, and this can happen when you delete , rename or move the profile folder or if you run firefox from a removable media storage device or when the profile folder is stored some where on the network.

Fix Cause #3 -  Fix the entry in profiles.ini in profile folder   

Search for the file named profiles.ini and you will find one at the following path

C:\Users\<vista username>\AppData\Roaming\Mozilla\Firefox

Open profiles.ini in notepad




It will look like the text written above, make sure the value of IsRelative=1 to load the default firefox profile and save it and try to start firefox. If still the problem persist then create a new profile with firefox profile manager and transfer the data from the locked profile to the new profile.

1. To create a new profile, press Windows Key + R to open run prompt

2. Type firefox.exe –p to open profile manager and create a new profile


Here is how you can transfer the data from your locked profile to new profile  in firefox or backup up your data through mozbackup


The most simple way to solve this problem is to end the firefox process (firefox.exe) shown in task manager under process tab, locate it, right click and select end process, open task manager by press ctrl+shift+esc or In my case I create a desktop shortcut to force kill firefox, here is how it can be done.

1. Right click on the empty area of the desktop and select new >> desktop shortcut

2. Now copy and paste the following path in the target box

C:\Windows\System32\taskkill.exe –f –im firefox.exe

Note: –f is for force kill and –im is to kill all instances of Firefox

3. Give a name to your shortcut and click Finish

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{ 7 comments… read them below or add one }

dar August 15, 2009 at 3:28 pm

-ya gotta wonder why Jack&Jill users have to jump thru hoops to get ff running properly:
why the rush to unleash an unstable release?
[oops, just remembered, the very same stuff happened many moons ago,when ff’s market share was a mere 8% …WHY?]

shaneecy August 16, 2009 at 6:58 pm

alternatively, , go to “Processes”, end the “firefox.exe” process, and restart firefox. this always fixes that error for me.

Richard June 14, 2010 at 3:48 pm

If there’s a running Firefox using the -no-remote command line option, that can also cause this error – removing this option fixes the problem.

umasankar November 6, 2010 at 11:07 am

Well, this is embarrassing.

Firefox is having trouble recovering your windows and tabs. This is usually caused by a recently opened web page.

You can try:

* Removing one or more tabs that you think may be causing the problem

* Starting an entirely new browsing session

madhusoodan April 23, 2012 at 9:38 am

Thanks for your help.. it worked for me :)

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