As a web developer, I would love to root for Firefox but they've made some really odd decisions regarding the implementation of web standards (which are published on the Mozilla MDN site, oddly enough), async/defer script loading order for example. Firefox is also often multiple years late with implementing new tech, being surpassed by Chromium and even Safari most of the time.
While I love the non-profit style of Mozilla and think competition in the browser space is a good thing. The reality is just that their browser lags behind the other two. Firefox is a large part of the reason polyfills are still used in this world of evergreen browsers, and requires multi-browser testing/tweaking even though I exclusively follow the standards written on the MDN website...
firefox (feddit.uk)