You're comparing apples and oranges...
- Firefox (all platforms): 2.74%
- Linux (all platforms): 1.61%
- Firefox (desktop): 6.64%
- Linux (desktop): 4.45%
You've chosen to compare Firefox's share from all platforms to Linux's share only on desktop. I don't know whether this was deliberate misinformation-pushing, or an innocent brainfart/inability to parse data, but that's not how data is compared.
Firefox has 50-70% more users than Linux, depending on the platform you use for comparison.
No matter how you cut it, Firefox is more popular. It's more popular across all platforms as a whole, and it's also more popular on desktop.
And 4.45% of a far smaller number is not greater than 2.74% of a much much larger number.