... and you are fully HTML5. No need for Flash, as you can still comment on video without Flash installed and watch content in HTML5 via this easy workaround.
Embedded videos will always be served as HTML5.
Youtube disables HTML5 in non-preview mode for A LOT of content, because they need to insert Ads and their Ads engine is not working on HTML5/WebM yet.
So if OP has opt-in'ed for monetarisation, thus turned on the Ads, and then only Flash is allowed.
You can also use extension (for Firefox; Chrome should have equivalents) such as Youtube Anywhere Player, that force HTML5.