Sure, most consumers have marched off desktop os entirely to walled garden mobile apps. That probably also means whats left of the desktop browser users are perhaps more likely to be firefox users than beforehand when it was more of a mass market.
Your imagination aside, the statistics show a decline in Firefox numbers, and it has a woefully small marketshare (~4% across all devices). It's been declining for 12 years. They lost ~50m users in ~3y.
"Techies" have or are moving on because Mozilla's pace of development is woeful, and compatibility is poor. Killing the RSS reader was the final straw for many. Disney advertising in-browser was another major moment.
