I think what he means is some elements are more specific than others in the DOM, or have a smaller scope. Since a textarea exists inside the body, any style defined for textarea will overwrite body{} styles. So FF's default textarea style overwrites your body style, even though yours is defined later (usually something more recent will take precedence, but not if it's in a broader scope/less specific).
I tried all sorts of tricks to stop textarea in mobile using a much larger font than the normal text. It seems that when my textarea was cols="45" the font was normal but as soon as it was raised to cols="71", even though it stayed inside the td tags the font grew large.
On the mozilla page ( https://developer.mozilla.org/en-US/docs/Web/CSS/text-size-adjust ) I found this
textarea {
text-size-adjust: none;
}
It seems to the best answer for me. It works on PC, tablet and, most importantly, on my android phone.
