For easy bookmarking (will open as a mini-browser) here's an example scriptlet: javascript:(function(){var w = window.open('https://play.google.com/music/listen#all',%20'GPlusMusic',%20'menubar=no,location=no,resizable=yes,scrollbars=yes,status=no');w.resizeTo(350,260);})();

(2014-06-24) FYI, for those noticing a somewhat lagging 'last updated'. It's still working with more than 6 months of use. As I'm using this extensively, chances are pretty good it'll be updated shortly after any requirements change.
(2015-05-26) Updated to work with recent material design update.
(2015-05-27) Time-played/remaining was blocking some buttons at the bottom. *fixed*
(2016-01-18) Updated styles with smaller window-size support (for use with 'application short-cut')
(2016-03-11) BUGFIX player controls were hidden due to updated styling by google.
BUGFIX Anoying hover-effects when mousing over album art.