SoundManager 2 makes it easier to play audio using JavaScript.
http://www.schillmania.com/projects/soundmanager2/

PxLoader is a Javascript library that helps you download images, sound files or anything else you need before you take a specific action on your site (like showing a user interface or starting a game). You can use it to create a preloader for HTML5 games and websites.

It let’s you monitor download status by providing progress and completed events and it lets you prioritize the order in which items are downloaded. You can even tag groups of files and then prioritize downloads or register for events by tag.

We created PxLoader for the HTML5 version of Cut the Rope and out of the box works great with images and sound files (the types of resources we needed for the game), but it’s designed to be extensible and work with any file type or other network action.
http://thinkpixellab.com/pxloader/

One of the goals of Firefox have always been to make the lives of web developers as easy and productive as possible, by providing tools and a very extensible web browser to enable people to create amazing things. The idea here is to list a lot of the tools and options available to you as web developers using Firefox.

Firefox – tons of tools for web developers!