I don't know what you do/sell on said websites, but if you still have a job it means that those who hired you haven't received (enough) complaints yet.
This might be due to Firefox users being more aware of standards than just "whatever runs on Chrome today", or because Google tends to ship non-standard behaviour with their browser and make it a "standard" with their massive marketshare. Or it might be related to Firefox developers implementing the standards more carefully in order to protect their shrinking marketshare.
In my experience people get way more complaints when the developer uses Chrome and the user uses Firefox than the other way around.
I was expecting that they perform their UAT on the prevalent browsers at the time. I don't expect/demand that people will UAT a website for "Pale Moon", but it is dangerous to not test Firefox, Safari, Chrome, Opera (and a few more) and in multiple devices/displays.
I have no expectation that a personal blog will display perfectly, but for some applications/websites every menu option, line, frame, must be perfecly visible as per the design, otherwise you get your Chrome users that cannot hit "send" to complete that funds transfer, and that won't keep you employed for long.
Regardless, I’m self-employed and my website makes enough money that I can spend plenty of time arguing with people on the Internet. Your admonishments certainly aren’t going to be my undoing.