It's too bad that Mozilla does everything they can to alienate its users, with failed attempts to attract a different but non-existent new user-base. Without them, and with Safari being run by a company that likes to tie its software to its hardware, there's pretty much no reasonable non-Chrome-based web browsers, so it's the new Internet Explorer, and many web pages only work on it, because no one tests their web pages on anything else.
With current standartization the issue of "page not working on non-Chrome browser" is non-existent. Thanks god nowadays everything (pages) work everywhere in very similar manner, I am using chrome, firefox, safary and opera and have zero problems last 5+ years. Old days are gone.
I simply have no idea why people hate on Firefox so much. I mean it, it feels like an outlet for frustration toward an org people think might listen.
People online rant about Firefox all the time for adding stuff Google and Microsoft shoved into their Chromium forks a few years ago, but when they do it the response is always "well what did you expect from <x>" while when Mozilla does it, the response is "this is an outrage, I'm switching to <some browser that already has the shitty feature anyway>".
I don't think there is or ever will be a "new internet explorer". If your page works in Chrome, there's a 99% chance it'll work in Firefox and Safari. Web standards have been unified to the point painting and layout algorithms are now part of the spec. It's why Ladybird managed to get a decently compatible engine in an extremely short time frame.