Firefox needs to work on ensuring seamless compatibility with more websites, web apps and so on, because I'm personally very bored with my kids' schools and related services sending out emails and forms with links that simply won't open in FF but are clearly expecting Chrome or Edge where they work fine. Yes, this is on the lazy developers, but if FF want wider scale take-up outside of geeky niche groups then this is the stuff they must fix.
Notepad++ and never look back.