What causes Firefox not to start and at those times I get this 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.

I am using Windows 7 Home Premium 64 bit. I do not recall the problem occurring when Windows 7 was first released. This has been happening for several months now with all versions of Firefox. 3, 4, and 5. I have searched online for a solution to this problem. I have tried every fix listed here and online that I could find. The problem remains. Does anyone have a fix for this?

The following may not completely eliminate having to terminate Firefox through the Windows Control Panel but it will come very close.
'''Plug-in and tasks started by Firefox may continue after attempting
to close Firefox''' The "X" in the upper right-hand corner closes the
Window (same as Ctrl+Shift+W) but even if it is the last Firefox window,
it does not necessarily close Firefox .
The only '''proper way to exit Firefox''' is to use '''Exit''' through the
File menu, not the "X" in the upper right corner of last Firefox window.
In the Beta that would be Alt+F then X
* '''Firefox hangs''' | Troubleshooting | Firefox Support http://support.mozilla.com/en-US/kb/Firefox%20hangs#w_hang-at-exit
Use the '''Windows Task Manger''' to remove all running firefox.exe in the "'''Processes'''" tab of the Windows Task Manager, then restart Firefox.
If Firefox will still not start, remove the parent.lock file from the profile which is created each time Firefox is started to prevent other Firefox tasks from running, see 
http://kb.mozillazine.org/Profile_in_use#Remove_the_profile_lock_file
'''Avoiding Problems with close/restart''' ''choose either extension''
:Use to close and restart Firefox after enabling or disabling an extension, switching to a new theme, or modifying configuration files, then you don't have to worry about delay or have to look in the Task Manager to see if Firefox is closed yet.
Both extensions use the same keyboard shortcut "'''Ctrl+Alt+R'''" or a file menu option.
*"'''Restartless Restart'''" extension for Firefox 4.0+ only (2 KB download ) https://addons.mozilla.org/firefox/addon/249342/
*"'''QuickRestart'''" extension (34 KB download) https://addons.mozilla.org/firefox/addon/3559/

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When i close firefox and then attempt to restart it i get the following message. firefox is alreadt running,but is not responding to open a new window.you must first close the existing firefox process or restart your system.

i have to restart

Sounds like Firefox is "hanging at exit". That problem is frequently caused by an Extension or a Plugin. Read all of the following articles. 
#Stop the Firefox process:
#*[http://kb.mozillazine.org/Kill_application Mozillazine - Kill application]
#*Windows 7 users click [http://www.techrepublic.com/blog/window-on-windows/reap-the-benefits-of-windows-7s-task-manager/2576 here]
#*Mac users: http://techheavy.com/2011/02/the-mac-task-manager/
#Why Firefox may hang:
#*[http://support.mozilla.com/en-US/kb/Firefox+hangs Firefox hangs] (see Hang at exit)
#*[http://kb.mozillazine.org/Firefox_hangs Firefox hangs (Mozillazine)] (see Hang at exit and Closing Firefox properly)
#*[https://support.mozilla.com/en-US/kb/Firefox+is+already+running+but+is+not+responding Firefox is already running but is not responding]
#Use Firefox Safe Mode to find a problem with an Extension or Plugin:
#*Don't check anything when entering Safe Mode, just continue
#*If the problem does not occur in Safe Mode it is probably and Extension or Plugin causing the problem
#*See:
#**[[Safe Mode]] and [http://kb.mozillazine.org/Safe_Mode Safe Mode (Mozillazine)]
#**[http://support.mozilla.com/en-US/kb/Troubleshooting+extensions+and+themes Troubleshooting extensions and themes]
#**[http://support.mozilla.com/en-US/kb/Troubleshooting+plugins Troubleshooting plugins]
#**[http://support.mozilla.com/en-US/kb/Basic+Troubleshooting Basic Troubleshooting]
'''If this reply solves your problem, please click "Solved It" next to this reply when signed-in to the forum.'''
Not related to your question, but...
You may need to update some plug-ins. Check your plug-ins and update as necessary:
*Plug-in check --> http://www.mozilla.org/en-US/plugincheck/
*Adobe Shockwave for Director Netscape plug-in: [https://support.mozilla.com/en-US/kb/Using%20the%20Shockwave%20plugin%20with%20Firefox#w_installing-shockwave Installing ('''''or Updating''''') the Shockwave plugin with Firefox]
*Adobe PDF Plug-In For Firefox and Netscape: [https://support.mozilla.com/en-US/kb/Using%20the%20Adobe%20Reader%20plugin%20with%20Firefox#w_installing-and-updating-adobe-reader Installing/Updating Adobe Reader in Firefox]
*Shockwave Flash (Adobe Flash or Flash): [https://support.mozilla.com/en-US/kb/Managing%20the%20Flash%20plugin#w_updating-flash Updating Flash in Firefox]
*Next Generation Java Plug-in for Mozilla browsers: [https://support.mozilla.com/en-US/kb/Using%20the%20Java%20plugin%20with%20Firefox#w_installing-or-updating-java Installing or Updating Java in Firefox]

I open firefox it keeps saying"Firefox is already running,but not responding.To open a new window,you must first close the existing Firefox process,or restart your system" i tried restart my computer...but it's still keep saying that..pls help me..

As I stated above, I have to constantly restart my computer because I get a message stating firefox is already running.

Do you see a firefox.exe in the Task manager if you look there right after you get this error message?
You do not have to restart the computer, just kill that process.
This situation may occur if Firefox was not closed correctly or crashed.

I try to launch firefox get the following message "firefox is already running, but is not resonding. to open a new window, you must first close the existing firefox process, or restart your system" firefox is not running and restart doesn't work

when I launch firefox get the following message "firefox is already running, but is not resonding. to open a new window, you must first close the existing firefox process, or restart your system" firefox not running and a restart doesn't solve the problem

Download a fresh Firefox copy and save the file to the desktop.
*Firefox 12.0.x: http://www.mozilla.org/en-US/firefox/all.html
Uninstall your current Firefox version, if possible.
*Do NOT remove personal data when you uninstall your current Firefox version, because all profile folders will be removed and you will also lose your personal data like bookmarks and passwords from profiles of other Firefox versions.
Remove the Firefox program folder before installing that newly downloaded copy of the Firefox installer.
*It is important to delete the Firefox program folder to remove all the files and make sure that there are no problems with files that were leftover after uninstalling.
*http://kb.mozillazine.org/Uninstalling_Firefox
Your bookmarks and other profile data are stored elsewhere in the Firefox Profile Folder and won't be affected by a reinstall, but make sure that you do not select to remove personal data if you uninstall Firefox.
*http://kb.mozillazine.org/Profile_folder_-_Firefox
See also:
*https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding
*http://kb.mozillazine.org/Profile_in_use
*http://kb.mozillazine.org/Recovering_a_missing_profile

I often get this message. Firefox is already running but is not responding.To open a new window you must first close the excisting Firefox process or restart your system.Thankyou Colin.

So this message appears mainly if I were changing web sites.Can't carry on until I have cleared everything from screen,gone on to my Thunderbird e-mail then Firefox will load again.I can then just carry on till next time.

Please look at [[Firefox is already running but is not responding]]
The initial problem is solved by killing any process firefox.exe, ( & maybe also plugincontainer.exe) Make sure you always close firefox by using the option Firefox Button -> Exit
You may need to investigate further and clear some of the duplicated files that may exist.

When I try to accessFirefox, I get a message that says Firefox is already running ,but is not responding.To open a new window,you must first close the

I get this message when I click the icon on the desktop or open a webpage from O.E.

Make sure that you do not start Firefox with the -no-remote switch appended to the command line.
* http://kb.mozillazine.org/Opening_a_new_instance_of_Firefox_with_another_profile
See also:
* http://kb.mozillazine.org/Profile_in_use
* [[Firefox is already running but is not responding]]

When I click to open firefox it says that "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" and I've tried to shut down and restart my computer but it keeps

when i click to open firefox it says that "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." and I've tried to shut down and restart my computer but it keeps showing the same message. I've even uninstalled Firefox and then reinstalled in the hopes that the problem would be solved but it this message is still popping up. What can I do to solve this problem?
== This happened ==
Just once or twice
== I was on facebook trying to upload pictures yesterday. ==
== User Agent ==
Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; .NET CLR 1.0.3705; .NET CLR 1.1.4322; Media Center PC 4.0; InfoPath.1)

Do you have a profile lock file in your profile folder? If so, delete it and see if TB runs properly:
http://kb.mozillazine.org/Profile_in_use#Remove_the_profile_lock_file

Firefox is OPEN and working fine, but when I click a link in Thunderbird I get '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.'

If I click a link on my desktop or in any other program (while Firefox is open and running), I get this 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." There's about a billion links for this if you Google it, but they all say that Firefox wasn't shut down properly. (OK, maybe not ALL of them, but if the needle is in that haystack, I haven't yet found it.) That's not the issue in my case since I haven't shut FF down at all.
== This happened ==
Every time Firefox opened
== IDK

This began to happen to me when I tried to run two separate profiles simultaneously on the same installation of firefox with -no-remote

Doesn't start when starting as administrator. Error 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.

Update firefox, it asked me to update flash, I tried to update flash but it said I had to close firefox. A box came up and said the Flash install would continue when I closed firefox. I closed all firefox windows and no update of flash occurred. I tried relaunching firefox but got the "Doesn't start when starting as administrator. Error 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." message. I rebooted the system, no improvement. I tried to run firefox as administrator and got the same message. Either I find a fix or I won't be able to use firefox and will have to go back to ie.

-> press '''CTRL''' + '''SHIFT''' + '''ESC''' to Open Task Manager -> Processes tab -> right-click '''firefox.exe''' and click '''End Process Tree''' -> close Task Manager
Troubleshooting extensions and themes
* https://support.mozilla.com/en-US/kb/Troubleshooting%20extensions%20and%20themes
Troubleshooting plugins
* https://support.mozilla.com/en-US/kb/Troubleshooting%20plugins
Check and tell if its working.

I deleted the profile and firefox4 and then downloaded firefox4 again. But when i click firefox it says 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.HELP!

somehow i couldn't get rid of one website called www.searchqu.com/405 set as my homepage... I tried all solutions given to change the homepage but whenever i restarted firefox that homepage used to come automatically.. So, I deleted the profile (even from recycle bin!!) and deleted the firefox and downloaded it again hoping to get my problems fixed (which didn't happen!) because i'm getting dialog box saying- 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.

You don't say which operating system you have installed?
Assuming it's Windows, right click a blank part of the Windows Taskbar and go to Task Manager. Then click the ''Processes ''tab, find '''firefox.exe''' and then right click it and choose '''End Process'''.

Iget this when I try to open a session....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.task mngr shows no open firefox processes.

I get this when I try to open a session....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.The task manager shows no open Firefox processes.I had two users on this laptop running Firefox and I tried deleting the program on both users. I then downloaded the newest version, installed it and I still get the error message as before. HELP!!!! I loved the browser program when it was working before and would rather use it than other browsers.

See "Hang at exit":
* http://kb.mozillazine.org/Firefox_hangs
* https://support.mozilla.com/kb/Firefox+hangs

I keep getting this message after closing Firefox and attempt to reopen-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.

I keep getting this message after closing Firefox and attempt to reopen-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.

See:
* http://kb.mozillazine.org/Recovering_a_missing_profile
* http://kb.mozillazine.org/Profile_in_use

When I try to start Firefox I get 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.

I get this message when I try to start Firefox after first logging on after turning on the computer.
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.
Have rebooted. Works when Administrator logs in, just does this in my user profile. Have also re-intalled. Mo change in my User account.
Firefox was working fine for the last 3 1/2 years. Any suggestions?

Firefox is "hanging at exit" when you exit/quit Firefox. 
#Stop the Firefox process:
#*[http://kb.mozillazine.org/Kill_application Mozillazine - Kill application]
#*Windows 7 users click [http://www.techrepublic.com/blog/window-on-windows/reap-the-benefits-of-windows-7s-task-manager/2576 here]
#*Mac users: http://techheavy.com/2011/02/the-mac-task-manager/
#Why Firefox may hang:
#*[http://support.mozilla.com/en-US/kb/Firefox+hangs Firefox hangs] (see Hang at exit)
#*[http://kb.mozillazine.org/Firefox_hangs Firefox hangs (Mozillazine)] (see Hang at exit and Closing Firefox properly)
#*[https://support.mozilla.com/en-US/kb/Firefox+is+already+running+but+is+not+responding Firefox is already running but is not responding]
#Use Firefox Safe Mode to find a problem with an Extension or Plugin:
#*Don't check anything when entering Safe Mode, just continue
#*If the problem does not occur in Safe Mode it is probably and Extension or Plugin causing the problem
#*See:
#**[[Safe Mode]] and [http://kb.mozillazine.org/Safe_Mode Safe Mode (Mozillazine)]
#**[http://support.mozilla.com/en-US/kb/Troubleshooting+extensions+and+themes Troubleshooting extensions and themes]
#**[http://support.mozilla.com/en-US/kb/Troubleshooting+plugins Troubleshooting plugins]
#**[http://support.mozilla.com/en-US/kb/Basic+Troubleshooting Basic Troubleshooting]
'''If this reply solves your problem, please click "Solved It" next to this reply when signed-in to the forum.'''

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. How do I fix this? I am ready to go back to internet explorer!

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 box appears and then firefox quits...never opens.
I have uninstalled, and loaded firefox 5 times and never got it to run.

See [[Firefox is already running but is not responding|Firefox is already running but is not responding]].

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. I have tried

After deleted profile my Firefox will not start
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.
I have tried – Restarting - Checking control panel for active firefox.exe –Uninstal l- Reinstall- and run CCleaner. All without any result
Can You help me? Are there any other processes that can be running?
Is there any cleaning tool available?
Best Regards, Pelle

Hi Pelle,
Why did you delete your profile? Also how? Did you use the profile manager or did you delete from the windows file structure?
It sounds like something during the profile delete has stopped Firefox from starting up. Please see the this article and follow the steps:
Please see this article: [http://kb.mozillazine.org/Profile_in_use]
--Edward

I getthe 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. It is NOT open I onlly have one computer

I installed FF on my new computer, Windows 7 Toshiba, I get the 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'''. It is NOT open I only have one computer.
I had a computer expert try everything and we cannot get it to open.

Look for the firefox process firefox.exe and kill it with for instance task manager. it is also worth watching for plugincontainer.exe.
The problem and solutions are explained in the articles:
* [[firefox is already running but is not responding]]
*[[firefox hangs]]

What causes Firefox not to start and at those times I get this 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.

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