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

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 systemProfile 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/MeC:\Windows\Application Data\Mozilla\ 
C:\Windows\Profiles\\Application Data\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 delayedshutdown 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
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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