here are some actual metrics from our ecommerce site (US, home remodeling / DIY):
if you look at desktop traffic only:
Nov 2015: 16.01%
Nov 2016: 13.27%
Nov 2017: 10.33%
Nov 2018: 8.14%
Desktop IE in Nov 2018 was 11.37%, Edge 15.65%, Chrome 52.74% and Safari 11.65%.
if you include mobile traffic (where Firefox is basically non-existent), then Nov 2018 is closer to 3.5%.
talk about bleak :(