Eric, this can happen after a failed update that partially changed your Firefox install directory.

Try a clean reinstall:

  1. Download the Firefox installer from Mozilla.com and save it to your desktop or other location.
  2. Make sure that Firefox is closed completely
  3. Delete the Firefox installation directory (On Windows, this is typically the C:\Program Files\Mozilla Firefox folder that contains "firefox.exe" and other Firefox program files and folders).
  4. Reinstall Firefox by running the installer you downloaded previously.

Your personal settings, including bookmarks and history, will not be lost.

See http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Clean_reinstall

Under Windows 7 I am also getting the following error message henc unable to start firefox at all: error message box as follows XULRunner Error: Platform version 1.9.2.4 is not compatibale with minVersion >=1.9.2.6 maxVersion Uninstalled, deleted subsdir, several times and with same results. Update must of corrupted other files

Did you delete the C:\Program Files\Mozilla Firefox folder ?

You can also try a custom install in another program folder (C:\Program Files\Mozilla Firefox36)