It would be really bad if everyone used Firefox - just as it would be very bad if everyone used Chrome (or even any other browser based on the same rendering engine). We all absolutely do benefit greatly from having multiple competing browsers and render engines - regardless of which one we individually prefer to use. Therefore I really don't understand the many, many, many "my-browser-is-better-than-yours-you-should…
Also because they say FF is better but... for what/who? what parts are better?
I try it a couple times a year, and always go back to Chrome, because the UX is so bad (for me). I get more stressed about the browser I'm using, than actually enjoying the browsing