When sites break, people leave Firefox. No amount of explaining or media changes that: the number one (by far) reason people leave a browser is because a site is broken.
Vista's added security measures like UAC (https://en.wikipedia.org/wiki/User_Account_Control) broke a lot of poorly coded Windows applications that didn't bother to follow the rules of the platform.
Who did the users blame when those apps broke? Microsoft.
Why? "It worked fine until I upgraded to Vista!"
Sigh.
I think they did improve the UAC situation with Vista SP1, if memory serves.
https://www.networkworld.com/article/2253987/microsoft--neut...
I seem to recall Vista was way more sluggish than 7 on the same machines.
But then again I guess i'm not an average user.