Some of the most notable new additions in HTML5 are the video tag that will let videos to be displayed directly in the browser without having to rely on plugins and Offline Storage. YouTube has a preview of it's HTML5 Video Player.
Web developers can benefit from proactively understanding & planning on incorporating HTML5 features in their websites. There are some good learning resources online for HTML5 -
Also see:
HOW TO disable Flash in IE and Firefox
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