I can stop music playing whilst out of the web browser but occasionally, I like to play my music whilst using the web browser. However, I can't find a way of stopping a track (e.g. for when I come across a video). Is it actually possible without quitting out of the web browser?

when in the browser press the ps button, it should bring you to the song your playing. but dont click the song, that will do nothing, instead go up the folder tell you get to the main "Music" folder/main list under the music icon in the XMB  then go up and the first icon is the one that controls the music in the background, click that and some standard options will pop up and click the stop button.