Another alternative may be FireAmp,a fully functional based on player and Winamp is installed as extension for Firefox.Almost a clone of Winamp is done in Java (if you do not have Java installed, you can download it from here and even supports Winamp skins from the classic 2, as shown in the picture below, using the skin Winamp Vista:
Once installed the extension to access the player via an icon on the toolbar In my case I had to add the icon because it did not appear by default, so you can add from the menu View - Toolbars - Customize ... and drag the icon to the toolbar. When opening the player will see something very similar to Winamp, another default skin, but with the same characteristics as the equalizer, playlist, and playback controls.You can add files and folders, upload and store lists the same way we do it in Winamp and similar programs.
The advantage of using Java is that it's multiplatform so no matter the operating system if you have Java installed.Disadvantage can be the consumption of resources, but may close the browser and continue the open player. Although it is not necessary and may open a desktop player, the idea in itself is interesting and well realized.