It was different in the case of IE though. It was actually atrocious and not standards compliant in many many ways.

Today, chrome and FF both support standards fairly well and when things don’t work in FF it’s usually either that you wrote fragile code, or there’s a slight difference from chrome that technically isn’t a standards compliance issue. Testing in both of those browsers isn’t hard and should be the norm. I’ve had projects where I had to test in IE, chrome windows, chrome android, FF, safari Mac, safari iPad OS, and safari iOS all at the same time. And yes there are differences between those last two, because apple makes a shitty web browser.

If you can’t test in two browsers, you’re just a bad web developer…