Like the article said: no one cares (more or less) about how good the browser is. If you have to go install a new browser, that's more work than just using the builtin one, and Google can force every Android phone to install Chrome out of the box.
Also, though I use Firefox mobile out of a desire to not be a part of the Chrome problem (even though I know it's useless and I'm not actually helping by doing so), it's not fast, and it's not nice to use. It's painfully slow, crashes much more frequently than the other browsers, has confusing settings and constantly promotes garbage like Pocket (which you can disable if you dig through the confusing settings, but you can't actually uninstall it), etc.
Until Mozilla gets the performance problems under control (and they're finally attempting to do this with Quantum et al.) they won't stop the bleeding. Unfortuantely, stopping the bleeding is the easy part: getting new users is the hard part and I tend to agree with the article that they don't have a way to do that on mobile (though I know nothing about marketing, so hopefully I'm wrong and just spouting nonsense here).