I'm pretty sure this used to be the 'right way' of doing things: use 'px' when the text shouldn't be resizable (apart from via page zoom) and 'em' when it shoul

I'm pretty sure this used to be the 'right way' of doing things: use 'px' when the text shouldn't be resizable (apart from via page zoom) and 'em' when it should be resizable. I speculate that the other browsers opted to make 'px' text resizable because a large number of sites use 'px' text, perhaps inadvertently due to lack of accessibility testing. So for these sites it's more user-friendly to make 'px' text resizable, than forcing the user to zoom the whole page.