Mozilla had a lot of goodwill, particularly in the tech world. With the right strategy, they could have translated that into thousands of influential websites encouraging users to use Firefox.

Things like releasing features for firefox users first, because devs like firefox and it had better devtools, would have kept the firefox userbase afloat.

Instead the mozilla devtools have been allowed to fall behind, web apps are no longer developed firefox-first, and mozilla lost it's opportunity.