Twitch.tv Full HTML5 Player
This is confirmed to work with Firefox 42 and newer with the latest Greasemonkey and Chrome 46 and newer with Tampermonkey.
Greasemonkey: https://addons.mozilla.org/en-us/firefox/addon/greasemonkey/
Tampermonkey: https://chrome.google.com/webstore/detail/tampermonkey/dhdgffkkebhmkfjojejmpbldmpobfkfo
1: First install the Greasemonkey addon (for Firefox) or the Tampermonkey addon (for Chrome)
2: Restart your browser
3: Left click on this link it should ask you about installing the script, click ok.
https://github.com/EchoDev/TwitchHTML5/raw/master/Twitch.user.js
4: You are done, you can disable Flash and use Twitch.tv in full HTML5
Note: To disable Flash in Firefox you can uninstall the Flash NPAPI plugin, to disable Flash in Chrome go to about:plugins and click the Disable button under Flash
Note 2: This script might not work when the FrankerFaceZ addon is enabled