Chrome is the only browser to support the Web Audio API (which isn't fully standardised yet anyway I don't think), but that is an amazing API for audio, and is far better than HTML5 audio.
Mozilla supports the Audio Data API which predates Chromes entry into that space: https://wiki.mozilla.org/Audio_Data_API
At some point this will be battled out in the W3C and a standard API will appear.
The two don't compare at all. The Audio Data API simply allows you to write custom sample data to audio buffers. The Web Audio API is a complete audio routing/processing graph complete with all the features you'd expect of a good audio engine. The Audio Data API is pretty useless for games compared to the Web Audio API.
The Audio Data API is terribly low level, and the current implementation in Firefox is so laggy that it's not an option for real-time game audio. Chrome's Web Audio should win this battle without a sweat.
