It's interesting that we are entering 2017 and the most popular configuration for users are...
But the stats cover Firefox users, not average PC users.
I'd guess there's a lot of overlap between (people savvy enough to keep old PCs in service) and (people savvy enough to download a browser that didn't come built-in to the system).
In particular, if you're using an older PC to browse the web, you're pretty likely to want to do some selective content blocking. I believe Firefox has more plugin options for that than the other big contenders.
Similarly, Firefox may be the best choice on Windows 7. But on a brand-new Windows 10 PC, many people may be satisfied with built-in Edge.
But the stats cover Firefox users, not average PC users.
I'd guess there's a lot of overlap between (people savvy enough to keep old PCs in service) and (people savvy enough to download a browser that didn't come built-in to the system).
In particular, if you're using an older PC to browse the web, you're pretty likely to want to do some selective content blocking. I believe Firefox has more plugin options for that than the other big contenders.
Similarly, Firefox may be the best choice on Windows 7. But on a brand-new Windows 10 PC, many people may be satisfied with built-in Edge.