I came to say this as well. The market share of Linux in the US is 5.03%, while the same for Firefox is 4.23%! [1]

It's not an apples to apples comparison. But the userbase is largely the same, and it's easier to switch a browser than it's to switch an OS. So it does have a significance.

[1] https://gs.statcounter.com/browser-market-share/all/united-s...