HTML5 video
Support for HTML5 video has been steadily increasing. In June 2013, Netflix added support for HTML5 video. In January 2015, YouTube switched to using HTML5 video instead of Flash by default. In December 2015, Facebook switched from Flash to HTML5 for all video content.
HTML5 in mobile devices
Offline support helps browsers cache static pages. They depend more on HTTP response headers sent by web servers to fetch HTML, CSS and multimedia required to render the web page. If everything required to render is cached, then a page loads quickly, but even if one item is not cached then everything slows down dramatically.