Earlier quoted context omitted.
Yeah, no; most times when you test in Firefox it works just fine with no changes; specially when you already tried on mobile, because if it works in mobile it works on desktop Firefox. The other thing is that major libraries (CSS, JS: jQuery, bootstrap, React) make sure they work on all browsers so you don't have to worry about that part. The winXP-IE6 was hell because that never happened, you always had to changes t…
I use Firefox on Android and often run into web sites that don't work right because they are dependent on some Chrome or Webkit behaviour, and I need to switch the browser to desktop mode to resolve the problem.
most web problems are now bugs either by the site developer or in a specific browser.
thats a long way from ie6 problems where either you needed a unique site configuration for every browser or supported ie6 only.