Is this a problem with Firefox on your Windows 7 computer?

Could you try starting up in Firefox's Safe Mode? That's a standard diagnostic tool to bypass interference by extensions (and some custom settings). More info: Diagnose Firefox issues using Troubleshoot Mode.

Hold down the Shift key on the keyboard while starting Firefox.

You should get a small dialog with two buttons. Click "Start in Safe Mode" (not Reset).

Any difference?

Thanks for the response. The solution might have worked. But at my workplace, I noticed Firefox version 26.0 is not supported. Therefore, I uninstalled the newer version and went back to version 24.0. It works now. Thanks.

Note that this is a problem with some files (likely .ini files) in the Firefox program folder not getting updated properly and you are left with a mixture of new and old files.

If you use ZoneAlarm Extreme Security then disable Virtualization and reinstall Firefox.
Other security software may have similar features to prevent Firefox from updating files properly.

See these pages for a similar issue with corrupted files:

• http://kb.mozillazine.org/Browser_will_not_start_up#XULRunner_error_after_an_update

• [/questions/880050]

What's weird is that Firefox 24 is also not in the specified range of 25.0.1 to 25.0.1. Maybe it's an IT thing?

By the way, if you have not discovered the Extended Support Release of Firefox 24 consider using that. When Firefox auto-updates with security fixes, you will get a later version of Firefox 24 instead of getting Firefox 26 again.

http://www.mozilla.org/en-US/firefox/organizations/

(You can skip Step 1)