The most depressing truth that I've mentioned as well on HN many times. Chrome is the new IE. I have never stopped using Firefox. I was an early Chrome user till I realized no adblock, then when adblock came it was weak and barely worked and gave up on Chrome altogether. Firefox has always had powerful customization without screwing the end user in the long run.

At least back in the mid 2000s if you ever saw banners that said a site needed Firefox to run properly it was because people were on IE which didn't support new standard HTML features. Not because devs didn't test their JS outside of Chrome. If you can't code for more than one browser you shouldn't be a web developer imho. Unless you're doing Electron or something.