Sounds like Firefox is "hanging at exit". That problem is frequently caused by an Extension or a Plugin. Read all of the following articles.

NOTE: Establish a habit of exiting/closing Firefox with Firefox button > Exit or File > Exit to allow an orderly shutdown of Firefox and closing of all of the files that Firefox has open.

1. Stop the Firefox process:
   • Mozillazine - Kill application
   • Windows 7 users click here
   • Mac users: http://techheavy.com/2011/02/the-mac-task-manager/
2. Why Firefox may hang:
   • Firefox hangs (see Hang at exit)
   • Firefox hangs (Mozillazine) (see Hang at exit and Closing Firefox properly)
   • Firefox is already running but is not responding
3. 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 an Extension or Plugin causing the problem
   • See:
     • Diagnose Firefox issues using Troubleshoot Mode and Safe Mode (Mozillazine)
     • Troubleshooting extensions and themes
     • Troubleshooting plugins
     • Basic Troubleshooting

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I too faced this issue sometime back, and it happened while i was trying to change/run Firefox with a different profile. Try this it should atleast open your browser

1) goto Run and type "firefox.exe -profilemanager" [or firefox.exe -P]

When it asks the you can try creating a new profile or try with the existing ones

2) Browse to C:\Users\"Your user_name"\AppData\Roaming\Mozilla\Firefox

Once there delete the 'Profiles' dir and also the 'profiles.ini' file.

Then try repeating STEP 1 above and create a new profile when asked

In worst case give the machine a restart and repeat from STEP 1

CAUTION: Prabhuti's post

Deleting the Profile folder (following step 2) in Prabhuti's post will delete all of your personal information (passwords, bookmarks, extensions, customizations). This should not be done. Only as a last resort is establishing a new Profile usually necessary. Keeping the old profile allows the user to retrieve certain important information (passwords, bookmarks) and copy them to the new profile.

The path shown in step 2 is not the path for XP.

The result of Prabhuti's post is starting clean like the initial installation of Firefox.

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