I created these backing tracks almost 10 years ago. Back then, the only reliable way to make the tracks playable directly in a web browser was to upload them on YouTube. Since then, a lot has changed and with WebAudio API being supported by all major browsers the options seem pretty much unlimited. I am currently working on several music related tools (aimed mainly at singers and guitarists). If you want to get notified once these are finished, consider subscribing to the YouTube channel I used for the original backing tracks. Cheers!