Windows that remain hidden

Hii..

I have two monitors and I run into this issue quite often. Where for some reason the application window in mac remains hidden. For eg. I can go to the menu of an application say 'Firefox' and select the 'Window' but the Firefox browser will not appear on any of my two monitor, the menu will remain active. There is no way to get to the window. Even via mission control. If i right-click on the Firefox browser in the dock and hit 'Show All Windows' it will show the open window in a border. Clicking on it will not bring it to the front but the remaining application will come back.

Please help..!

I didn't find the right solution from the Internet.

References:-
https://goo.gl/hRTozH
Healthcare advertising video

Thanks!