When I run a html file with an embedded cdf file, I get the request that I should install cdf player. Both my computers already have cdf player installed. A specific example of this is in the file http://www.abstractmath.org/MM/Mathematica/RiemannSumExp.html
The code in the was created by Mathematica 10.2. I have posted many other html files that contain embedded cdf files which produce the same results. They were made with previous versions of Mathematica. A couple of them are
http://www.abstractmath.org/Word%20Press/?p=4532 (published in 2012)
All the files I published worked properly until about six months ago.