The YouTube website support these days only HTML5 video player, and the YouTube Flash support is soon ended. Because most web browsers will not add anymore the NPAPI plugin (the Adobe Flash player) in his web browser.
How get the YouTube Flash?
In Google Chrome will the browser manage itself the flash update for each new web browser version. In Chrome v56 is Adobe Flash support ended. While in Opera you can use the Flash player if you go to the Adobe Official website and download theire the latest version.
Want to try this free extension, go to your web browser extension website: