is there an error message showing up / what does it say exactly? also make sure that you're always downloading the firefox setup file from the official location - getfirefox.com!

Sounds like Firefox is "hanging at exit". That problem is frequently caused by an Extension or a Plugin. Read all of the following articles.<br /><br /> 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. #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.org/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.org/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 an Extension or Plugin causing the problem #*See: #**[[Safe Mode]] and [http://kb.mozillazine.org/Safe_Mode Safe Mode (Mozillazine)] #**[http://support.mozilla.org/en-US/kb/Troubleshooting+extensions+and+themes Troubleshooting extensions and themes] #**[http://support.mozilla.org/en-US/kb/Troubleshooting+plugins Troubleshooting plugins] #**[http://support.mozilla.org/en-US/kb/Basic+Troubleshooting Basic Troubleshooting] '''If this reply solves your problem, please click "Solved It" next to this reply when <u>signed-in</u> 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.org/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.org/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.org/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.org/en-US/kb/Using%20the%20Java%20plugin%20with%20Firefox#w_installing-or-updating-java Installing or Updating Java in Firefox]

You can also try to reboot Windows or reboot in Safe mode (F8) to see if that allows to install Firefox.