Well, yes and no. It does matter because if they had spent that money and effort on the browser and made it possible to donate directly to the browser project then there is a fair chance that those numbers would be better.
Is it? Firefox has had this sheen of "jank" for the past 6 years.
Have you used it? I've used it as my primary browser for both personal use and web development for years and it has not been janky, at all.
I don’t know where that comes from, Firefox has worked just fine for ages. The only place it sucks is on iOS.
What exactly do you mean?
I use Firefox as a daily driver and it just works.