Tried Chrome 61.0.3163.100 and Firefox 55.0.3 on Mac OS X 10.12.6.

Load any song or album or playlist, press play. The icon changes to the pause icon, the album art goes grey and gets a pause icon overlay, the track gets a speaker icon next to it instead of the play button. But the song doesn't play and the track progress bar doesn't move from 0:00.

I can click on any time in the track and the track progress bar stays where it is as though the song is paused.

In Chrome's dev tools there is a single message in the console: "web-player.cf8d6aa7.js:1 It is recommended that a robustness level be specified. Not specifying the robustness level could result in unexpected behavior, potentially including failure to play." Failure to play is exactly what's happening.

Screenshot attached.