Using Chrome and the play button, I can move to the button and to other buttons on the page.  Perhaps with Firefox, that can't be done.

Marcio,

          This is a very strange site indeed in that the play buttons do not even get visited when brute force tabbing through the page.   When I looked at the page source, it turns out that they have used ARIA labels for each and every play button for the tracks listed.  For example, the track called Desensitized has an ARIA label on its play button, "Play Desensitized".

          I don't know whether that will help in any way, but it's the best I can do.  I have not previously encountered a music player page where the actual buttons that control play are not visited.

--

Brian - Windows 10 Home, 64-Bit, Version 1809, Build 17763  

A great deal of intelligence can be invested in ignorance when the need for illusion is deep.

          ~ Saul Bellow, To Jerusalem and Back