Thanks for that opinion. Now let me give you mine.
I first started making websites (or rather what we thought of websites back then; you wouldn't recognice them as such today) using HoTMetaL 1.0 and Mosaic on Windows 3.1. So I've been around the block a few times.
Two years later I was making corporate websites full-time, for an organization that had customers of all sorts all over the world, some of which used the latest kit, some of which were on low speed dial-up with obsolete software running on underpowered computers with low resolution screens. I was working on a Sparcstation with the biggest monitor I've ever used. I hand-coded HTML and CGI scripts (PHP was still in diapers) and the browser wars were in full swing. So as far as the principle is concerned that a good website should be client-agnostic, have no expectations on anything that goes on a the user side, and should work no matter what, I sort of get that.
Which is where my main gripe with this article and the various comments comes in.
This is not a case of a browser such as Firefox working badly. This is a case of website developers, after all these years, still being green kits straight out of school who think that because they can use a HTML editor or (gasp!) hand-code some HTML or PHP without breaking everything they are now qualified to make a public-facing production website. They are not.
Web 2.0 (to dredge up an old buzz-word) is a good thing; technologies such as Javascript and CSS reaching maturity to the point where interactive features became production-ready gave rise to anything from Facebook to Wordpress to the ChatGPT UI. But that does not mean that it is a good idea to load (and over-load) every website under the sun with tons of Javascript and simply expect that everyone will have the latest Wundermachinen with a water-cooled 16-core CPU and a GPU that can keep your coffee hot all day, and it also does not mean that you can simply expect their browser to excel at running and rendering al that crap.
In case you've missed it: Firefox is STILL a good browser. The fact that most website developers have become lazy and simply code for Chrome-based browsers is a different matter entirely. (And whoever makes a website that claims a certain browser is "unsupported" has always been instantly fired from my teams.)
Yes, Mozilla worries me. Management obviously is lagging behind in the race of keeping up with the neighbours and not responding well. And (as is so often the case) principles such as privacy get jettisoned pretty quickly in favour of better chances to make profits. But FF is still my standard for proper standards support, and infinitely better than using a Chrome based browser and handing all your privacy over to Google. Which also ditched their principles of "Don't be evil" when profits became more important, so if that's your argument then Crome and all its derivatives should also be ditched.
I know many here have sung Vivaldi's praises, but I do note that its add-ons (which for me make or break a browser, since I rely heavily on some of them) come from the Chrome Web Store. OK, maybe I'm paranoid or seeing ghosts here, but still. If Chrome comes with security concerns (and it SO does!) then I'm loathe to trust add-ons from the Chrome Web Store as well.
So, no. I'll stick with Firefox until it stops working or they pry it out of my cold, dead fingers. Declaring it "done" and suggesting that we all switch to something Chrome-based instead (which is pretty much the only alternative save for Vivaldi) seems a little daft to me. But then, the author of this "opinion" tells us all in great details what's wrong with FF but fails to point out what we should do instead.
If that's what passes for an opinion these days, mine should not be much worse.