malins
Stumbling Seeker
I think it's Xenforo's fault.I'm a little surprised that the site is pumping out old code,
The most direct way is just to get the recommended embed code off of youtube by right-click. That's got to be their up-to-date standard. It looks like this:
HTML:
<iframe width="500" height="300" src="https://www.youtube.com/embed/WuJE40OBt48" frameborder="0" allowfullscreen></iframe>
when I throw the raw code of both versions onto a featureless sample page, https://jsfiddle.net/o5powhhy/, Firefox will still turn the Flash object code into an HTML player, - both versions will play - so that must be a built-in script...?
Running that sample page from the desktop (it won't load Flash when run from within jsfiddle) I can reproduce the exact behaviour on the forum, I get Madiosi's screenshot result for IE and Chrome with the object code, automagically displayed HTML 5 player for Firefox with the object code, but - perfect HTML5 video for all browsers with the iframe code.
So this forum installation simply seems to be producing outdated code. It should be outputting the iframe code and then there wouldn't be any trouble with any major browser.
It might be worth checking whether video embed codes are produced by some kind of plugin or extension to the core system, such a plugin might need a separate update - or if the embed code is generated using editable templates for the code snippets, which might be easily fixed.