Otherwise use Start Menu and type firefox in the search bar.
When you see Mozilla Firefox in the Programs category right click on the program and choose Properties. The Application target location is what you need in the shortcut.
It will probably look like this: "C:\Program Files(x86)\Mozilla Firefox\firefox.exe"
Right click to edit the shortcut properties to match what you found in the target location.
that is probably due to registry errors.I advise you to download this software from http "://download.cnet.com/Free-Window-Registry-Repair/3000-2086_4-10606555.html" and then click on full scan and then fix errors .If it does not fix the problem, please reply.