Depends on which standards, for some css functions like backdrop-filters and mix-blend-modes it was years ahead of Firefox, where some of those had to be activated through about:config. I‘m glad Firefox catchend up in the past few years though. Also WebKit accelerated HTML5 adoption a lot.
Never had any major issues developing for Firefox, safari and chrome in the past few years though. It was quite a different story 10 years ago but nowadays 99% of the time, it works flawlessly between all major browsers for me.