Amazon Video
Customers of Amazon Video can stream on the web using an HTML5 player (supported in Chrome, Firefox, Internet Explorer 11, Edge, Safari and Opera).
Adobe Flash
Firefox (from version 46) rewrites old Flash-only YouTube embed code into YouTube's modern embedded player that is capable of using either HTML5 or Flash. Such embed code is used by non-YouTube sites to embed YouTube's videos, and can still be encountered, for example, on old blogs and forums.