downloads add pdf problem

Hi,
I´m using the newest firefox and found out a problem when I want to add file PDF to Downloads, it gives me an error that this file is no supported. I had set right everything so I was searching for a problem and found out that in Chrome works everything ok so I can add PDF file without problem.

Does anyone know how to fix this problem on Firefox. It is very strange.

Thank you.

Where does this error occur?