Nope, I've done an upgrade from win7 to win10 which already had the activeX items installed. Also, I did a clean install onto the same laptop (today) with win10.iso and I had to download the add-on for the firefox.
It asked me to logon to sling and works just fine. I also used the chrome webplayer (which I dislike) and it also placed the add-on just fine. try creating another local win10 profile. if that works under the new profile, you'll have to start using that one and ditch the other.