/**
 * MediaKeys namespace.
 */
if (typeof MediaKeys == "undefined") var MediaKeys = {};

MediaKeys.playButton = "//button[contains(@class,'spoticon-play-32') and contains(@class, 'control-button')]";
MediaKeys.pauseButton = "//button[contains(@class,'spoticon-pause-32') and contains(@class, 'control-button')]";
MediaKeys.skipButton = "//button[contains(@class,'spoticon-skip-forward-24') and contains(@class, 'control-button')]";
MediaKeys.previousButton = "//button[contains(@class,'spoticon-skip-back-24') and contains(@class, 'control-button')]";

/**
 * MediaKeys namespace.
 */
if (typeof MediaKeys == "undefined") var MediaKeys = {};

MediaKeys.playButton = "//button[contains(concat(' ', normalize-space(@class), ' '), ' spoticon-play-')]";
MediaKeys.pauseButton = "//button[contains(concat(' ', normalize-space(@class), ' '), ' spoticon-pause-')]";
MediaKeys.skipButton = "//button[contains(concat(' ', normalize-space(@class), ' '), ' spoticon-skip-forward-')]";
MediaKeys.previousButton = "//button[contains(concat(' ', normalize-space(@class), ' '), ' spoticon-skip-back-')]";

Update open.spotify.com-view.js