Source: http://arstechnica.com/gadgets/2015/01/y...

Everyone hates Flash, right? You have to install a plug-in, it's resource intensive, it doesn't work on mobile, and it causes all sorts of security problems. YouTube has been working on ridding itself of Adobe's ancient Web plug-in for several years now, and while the whole site has been slowly transitioning away from Flash, today YouTube announced it has finally serves HTML5 video by default. Users of Chrome, IE 11, Safari 8 and "beta versions of Firefox" will all have a Flash-less experience.

YouTube's transition seems to have been pretty straightforward. Four years ago, YouTube laid out alaundry list of problems it had with HTML5, and today it has a blog post explaining how it has worked with the web community to solve each issue.