Certain Firefox problems can be solved by performing a Clean reinstall. This means you remove Firefox program files and then reinstall Firefox. A clean reinstall is not the same as a regular reinstall performed using the built in installer. Please follow these steps:

Note: You might want to print these steps or view them in another browser.

1. Download the latest Desktop version of Firefox from mozilla.org (or choose the download for your operating system and language from this page) and save the setup file to your computer.
2. After the download finishes, close all Firefox windows (or open the Firefox menu and click the close button ).
3. Delete the Firefox installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Firefox
     • C:\Program Files (x86)\Mozilla Firefox
4. Now, go ahead and reinstall Firefox:
   1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to directly open Firefox after clicking the Finish button.

More information about reinstalling Firefox can be found here.

WARNING: Do not use a third party uninstaller as part of this process. Doing so could permanently delete your Firefox profile data, including but not limited to, extensions, cache, cookies, bookmarks, personal settings and saved passwords. These cannot be easily recovered unless they have been backed up to an external device! See Back up and restore information in Firefox profiles.

Please report back to say if this helped you!

Thank you.

DancingBetty said

My computer is set to auto update for Windows 7 Home Premium and for Microsoft Office Professional Plus 2010. I am also running Norton 360. There was a major update for Office on 12/10/14 that seems to be when my problems started. This month, every time my updates have caused a reboot, Mozilla has failed to open. I have uninstalled it and reinstalled it several times, and it has only lasted a day or two before it crashes again. This last time it will still not open. All the instructions to troubleshoot seem to be based on the idea that the program is open and just has issues. I can't even get it to open up in Safe Mode. I have tried to reinstall, and it says that it will launch automatically when the install is complete, but it is not working. Since Norton scans every download before it runs, I'm not certain if that is where the problem is since I never get the window that shows the step by step installer for Firefox. What do I need to do?

Thank you for responding so quickly to my question. My daughter arrived just as I was attempting to implement your suggestions. She was able to restore Firefox to a previous version and get me moving again. Hopefully this time the repair will "stick" and I won't be doing this again right away.

Good to hear that the issue was solved. Thanks for contacting the Mozilla support team. Have a happy holidays.

Window 7 Pro

I had Firefox Running (34.0.5) and now it will not open 

I have rebooted, restarted Nothing changed I uninstalled rebooted, reinstalled rebooted, hard start and nothing changed.

I have tried the solution suggested by removing the Mozilla Firefox folders from "C:\Program Files (x86)\Mozilla Firefox". We are still dead on FireFox. Any help appreciated. thanks

@cil1

If the above information does not resolve your issue, please consider creating a new thread containing the specific details of your issue.

Doing so will allow the Mozilla volunteers to give you solutions that are more helpful to you. This may help them to solve your problem faster and more efficiently.

Please, feel free to post the link to your thread on this thread for volunteers interested in assisting you.

Thank you.