If you specify your font sizes relatively, then you get the benefit of easy zooming in IE. But the problem is that your fonts will be different sizes in FF and IE, which can give you problems if any of your elements are precisely placed (or if you just want your pages to look the same).

Fortunately, there's a simple solution. Just set a default minimum font-size in your body declaration, thus:

body { font-size: 12px; }

Then you can size elements relatively

p { font-size: 1.5em; }

h1 { font-size: xx-large; }

And everything will scale consistently. Yay!