see https://support.mozilla.com/en-US/questions/833433

Sounds like it is hanging when you exit and later try to restart Firefox. This can happen even when choosing to restart during an update process. * How to stop the running Firefox process ** In Task Manager, does firefox.exe show in the '''<u>Processes</u>''' tab? ** See: http://kb.mozillazine.org/Kill_application **Windows 7 users: http://www.techrepublic.com/blog/window-on-windows/reap-the-benefits-of-windows-7s-task-manager/2576 * 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: ***See: ****https://support.mozilla.com/en-US/kb/Safe%20Mode ****http://kb.mozillazine.org/Safe_Mode ***Firefox 4 users, hold the Shift key while clicking the Firefox 4 desktop icon to enter Safe Mode. ***Firefox Safe Mode is a diagnostic mode that disables Extensions and some other features of Firefox. ****In Firefox 4, Safe Mode also disables Plugins and Hardware Acceleration. ****If you are using a theme, switch to the DEFAULT theme: Tools > Add-ons > Themes '''<u>before</u>''' starting Safe Mode (In Firefox 4, Tools > Add-ons > Appearance). See: http://support.mozilla.com/en-US/kb/Using%20themes%20with%20Firefox#w_managing-themes-and-personas ****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 '''<u>one at a time</u>''' until the problem reappears. ***#You can also enable a few at a time (3-5), keeping track of what you just re-enabled to see if the problem re-occurs; this will help narrow down the possibilities if you have a large number of add-ons. ***#'''<u>You MUST close and restart Firefox after EACH change</u>''' 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 <br /> -------------------------- <br /> '''You need to update the following.''' The Plugin version(s) shown below was/were submitted with your question and is/are out of date. You should update to avoid known security issues with the version(s) you have installed. Click on "More system info..." to the right of your question to see what was included with your question. *Shockwave Flash 10.2 r159 *Next Generation Java Plug-in 1.6.0_24 for Mozilla browsers #'''''Check your plugin versions''''' on either of the following links': #*http://www.mozilla.com/en-US/plugincheck/ #*https://www-trunk.stage.mozilla.com/en-US/plugincheck/ #*'''Note: plugin check page does not have information on all plugin versions''' #*There are plugin specific testing links available from this page: #**http://kb.mozillazine.org/Testing_plugins #'''Update the [[Managing the Flash plugin|Flash]] plugin''' to the latest version. #*Download and SAVE to your Desktop so you can find the installer later #*If you do not have the current version, click on the "Player Download Center" link on the "'''Download and information'''" or "'''Download Manual installers'''" below #*After download is complete, exit Firefox #*Click on the installer you just downloaded and install #**Windows 7 and Vista: may need to right-click the installer and choose "Run as Administrator" #*Start Firefox and check your version again or test the installation by going back to the download link below #*'''Download and information''': http://www.adobe.com/software/flash/about/ #**Use Firefox to go to the above site to update the Firefox plugin (will also install plugin for most other browsers; except IE) #**Use IE to go to the above site to update the IE ActiveX #*'''Download Manual installers'''. #**http://kb2.adobe.com/cps/191/tn_19166.html#main_ManualInstaller #**Note separate links for: #***Plugin for Firefox and most other browsers #***ActiveX for IE #'''Update the [[Java]] plugin''' to the latest version. #*Download site: http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE) #**'''''Be sure to <u>un-check the Yahoo Toolbar</u> option during the install if you do not want it installed. #*Also see "Manual Update" in this article to update from the Java Control Panel in Windows Control Panel: http://support.mozilla.com/en-US/kb/Using+the+Java+plugin+with+Firefox#Updates #* Removing old versions (if needed): http://www.java.com/en/download/faq/remove_olderversions.xml #* Remove multiple Java Console extensions (if needed): http://kb.mozillazine.org/Firefox_:_FAQs_:_Install_Java#Multiple_Java_Console_extensions #*Java Test: http://www.java.com/en/download/help/testvm.xml