Firefox is going to be the first major web-browser at long last to provide native support for the lossless FLAC audio codec. Per this thread, the support is ready and has landed in time for Firefox 51. FLAC support is integrated, including for HTML audio elements to utilize FLAC.
Great to see this finally happen but too bad Chrome doesn't yet support FLAC on the desktop and doesn't appear they are actively working on it. Microsoft's Edge also doesn't yet have native FLAC support.