-> Close Firefox (ALT + F -> Exit)

Start Firefox in Safe Mode by Holding down SHIFT key while starting Firefox

As an alternative method, select "Windows Start Menu -> Run" or press Win + R key combination and enter one of the following in the Windows Run box:

    firefox -safe-mode
    "C:\Program Files\Mozilla Firefox\firefox.exe" -safe-mode 

-> Firefox Safe Mode window will appear -> DON'T SELECT ANY OPTIONS, just click Continue in Safe Mode

Check and tell if its working.

In the safe mode there is only one occasion of the "Options" box. However, in normal mode there are two. The first one is the 4th dropdown under "Tools." A 2nd one occurs in the 11th (last) dropdown. Both give the same results, but I don't understand why there are two. I've tried getting a print screen of the box, but always closes when I press the alt key

You need to figure out which add-on is adding that 2nd Options menu item, see this:
https://support.mozilla.com/en-US/kb/troubleshooting%20extensions%20and%20themes#w_test-for-faulty-extensions