>>Testing on Chrome would save you from accidentally using Chrome-only features, but that's only part of the problem,
>How?
Sorry I meant "Firefox" and "Chrome-only" there.
In general though it's not like Firefox is spec compliant and others aren't, pretty much every browser works a little different in some areas. Just for the sake of saying something verifiable: no browser is spec compliant because the spec mandates a precise maximum length for strings and each main browser has a different, arbitrary (= I have the RAM, they just won't let me use it), lower limit on that.
How?
> caniuse.com kinda works better for that as you get data about other browsers too.
caniuse.com is nice but unlike using a standards compliant browser it requires you to be mentally alert and aware of it.
Using a standards compliant browser means you'll see the result of sloppy css immediately on the screen.