Play button (media buttons) behavior has changed for the worse.
On MacOs High Sierra the play button and next and prev (media buttons in the top of keyboard) are controlling what is in the main window and not my music from Spotify or iTunes.
This removes the idea of the button as I now have to open iTunes and then pause the music. Before I could just press the button when in Safari to pause the music
If I am on youtube it now pauses he video, that before could be done with just a mouse click
Please let us choose in preferences -> keyboard how these buttons behave.
MacBook Pro with Retina display, macOS High Sierra (10.13)