You will need to find and kill firefox.exe using Task Manager, see "Firefox is already running but is not responding" error - How to fix.

I personally consider it good practice to use Profile Manger ( see Managing Profiles ) to create a new profile and run separate versions of Firefox each with separate unique profiles, as explained in http://kb.mozillazine.org/Testing_pre-release_versions

Thanks for your kind response. But,the firefox.exe is not showing on the Task Manager? thanks again

If you get that sort of error message firefox.exe should be running. In Task manager did you

1. click the Processes tab
2. click the image name colun to sort by image name
3. you may need to scroll to find firefox.exe

John99, That is what I did and firefox.exe does not appear on this list?

What is the exact message that you get and when ?

Did you look at"Firefox is already running but is not responding" error - How to fix If you are not finding firefox.exe then rather than firefox hanging maybe it is actually crashing. So if firefox is crashing read Troubleshoot Firefox crashes (closing or quitting unexpectedly)

Same thing is happening to me and i have checked task manager up and down there is no firefox process running. I also restarted my computer 3 times already hoping that what ever is causing it to hang would stop. Not sure what else too do about to uninstall it and give up.

The exact message is "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.

Which there is no process to close and i restarted few times already any help?

If you can not find firefox.exe process after a warning that it is hung, either it has crashed, or the hang has sorted itself out and it has exited. The advice in the linked article is

Note: If this is a recurring problem, see Firefox hangs or is not responding - How to fix - Hang at exit for possible causes and solutions. It probably helps to set up a new profile, at least as a temporary test measure. If you do that I suggest using a names such as test-ff3 and test-ff4. Also it is wise to use individual empty folders for each profile.

I finally realised that the "show processes from all users" checkbox was not ticked at the bottom of task manager. (Although why firefox wasn't running in the default profile is a mystery)

The Windows show processes from all users in task Manager will; if you are in an admin account, show other accounts and their processes. That would tend to imply you are using firefox in more than one OS account.

Each separate OS account will have its own Firefox profile.

Does not help. "show processes from all users" was ticked but still it does not show up when crashing. Thanks for trying.

(I thought I had replied, guess I closed it without confirming)

If firefox is giving a message about it running then you should be able to find it with task Manager. (Unless it happens to crash or exit before you complete checking). If firefox is not running then you should be able to start it.

If on the other hand firefox has crashed it should generate reports and you should be able to obtain a crash signature.

Can you confirm what is happening, explaining what you see as firefox starts up, any error messages you get, and when you see them, and the reason that you say firefox crashed, again with what you see and any error message.

John99, I completely reinstalled firefox and started it. As soon as I click it launches the error message box:

"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"

With this message on, the task bar will show firefox.exe. but when the message is deleted the .exe file disappears. There are no other error messages or reports, unless you tell me where to look for a report.

OK so it appears Firefox is locking up and not responding rather than crashing.

1. You will need to figure out how to start firefox in its safe mode
2. You may need to be able to create and use a new firefox profile

Diagnose Firefox issues using Troubleshoot Mode <-- clickable link --- Read the article, try starting in safe mode, first of all try by using the option you should have from Vista.

• First of all check with Task Manger that firefox.exe is not running as a process
• Now try to start firefox - Do you see that option and does it seem to work ?
• Do you get the dialogue window with the options in a checklist
  • if so when starting SafeMode do not make changes, just click the continue button
  • does it work and open firefox, possibly at your home page ?

CARE
Note some further actions could cause you to loose information such as saved passwords and bookmarks used by firefox. Presumably you have previously used firefox on the same machine and have such data that you may want to keep. Is this presumption correct ?
I ask because normally steps will be taken to preserve such data whenever possible.