Firefox not closing completely (hanging at exit) is frequently caused by an extension or a plug-in.

• How to stop the running Firefox process
  • In Task Manager, does firefox.exe show in the Processes tab?
  • See: http://kb.mozillazine.org/Kill_application
• What may cause Firefox to hang at exit
  • http://support.mozilla.com/en-US/kb/Firefox+hangs
  • http://kb.mozillazine.org/Firefox_hangs
  • https://support.mozilla.com/en-US/kb/Firefox+is+already+running+but+is+not+responding
• You may need to try Firefox Safe Mode
  • You may need to use Safe Mode to locate the problem: http://support.mozilla.com/en-US/kb/Safe+Mode
  • Firefox Safe Mode is a diagnostic mode that disables Extensions and some other features of Firefox. If you are using a theme, switch to the DEFAULT theme: Tools > Add-ons > Themes before starting Safe Mode. When entering Safe Mode, do not check any items on the entry window, just click "Continue in Safe Mode". Test to see if the problem you are experiencing is corrected.
  • If the problem does not occur in Safe-mode then disable all of your Extensions and Plug-ins and then try to find which is causing it by enabling one at a time until the problem reappears. You MUST close and restart Firefox after EACH change via File > Restart Firefox (on Mac: Firefox > Quit). You can use "Disable all add-ons" on the Safe mode start window.
  • See the following for more information
    • http://support.mozilla.com/en-US/kb/Troubleshooting+extensions+and+themes
    • http://support.mozilla.com/en-US/kb/Troubleshooting+plugins
    • http://support.mozilla.com/en-US/kb/Basic+Troubleshooting

You need to update your plugins. It is important to keep them updated due to continuing security fixes and improvements in those plug-ins:

• Adobe PDF Plug-In For Firefox and Netscape "9.3.3"

1. Check your plugin versions: http://www.mozilla.com/en-US/plugincheck/
   • Note: plugin check page does not have information on all plugin versions
   • NOTE: A new security update for Adobe Reader 9.3.4 is due to be released 2010-10-05
2. Update Adobe Reader (PDF plugin):
   • From within your existing Adobe Reader (if you have it already installed):
     • Open the Adobe Reader program from your Programs list
     • Click Help > Check for Updates
     • Follow the prompts for updating
     • If this method works for you, skip the "Download complete installer" section below and proceed to "After the installation" below
   • Download complete installer (if you do NOT have Adobe Reader installed):
     • Use Firefox to download and SAVE the installer to your hard drive from the link in the article below
     • On the Adobe page, un-check any extra items (i.e. Free McAfee® Security Scan Plus) then click Download button
     • If you see message just under tabs, DO NOT click the Allow button, instead click below that where it says "click here to download".
     • Click "Save to File"; save to your Desktop (so you can find it)
     • After download completes, close Firefox
     • Click the installer you just downloaded and allow the install to continue
       • Note: Vista and Win7 users may need to right-click the installer and choose "Run as Administrator"
     • Download link and more information: https://support.mozilla.com/en-US/kb/Using+the+Adobe+Reader+plugin+with+Firefox#Installing_and_updating_Adobe_Reader
   • After the installation, start Firefox and check your version again.

I thank all of those who sent in suggestions (I would have gotten back to you sooner but life and some emergency surgery got in my way.). I will try sthese possible solutions and write a reply again afterwards. Thanks again.

P.S. I discovered earlier today that while having Windows Task Manager open I tried to open Firefox twice, Thunderbird once and Internet Explorer twice and the result of all 5 tries opened the 'Firefox.exe *32' file (twice), the Thunderbird.exe *32 (once) and the iexplore.exe files in Processes but did not opn those programs in Applications?? I had to restart my pc (an excruciatingly slow process) before I could actually open Firefox and get to these helpful pages.

I was having this same problem with both firefox.exe and iexplore.exe. It turns out that it was the Skype Click to Call plugin/addon was the problem. Everything worked fine once I uninstalled it.

@ winchesterlyon. Thanks! That did the trick!

It was a bit of a painful process as I was kind of in an infinite loop with the stuck firefox.exe*32 process. What worked was starting firefox in safe mode (hold down shift key and click firefox launcher) and select "Disable all add-ons" and "Make Changes and Restart". Then in the restarted firefox, go to the add-ons and disable Skype click to call. Hope help others...