If View is not 100%, the content of IFRAME elements is not scaled. Try to load the form.html attachment with View >100%, and look at the frame content. Analogosouly (but maybe this is a design choice?) the checkbox control does not scale, even at 200%.
Reporter, what version are you using ? See Help | About Mozilla. Worksforme in build 2002092708 (1.2a+) on Mac OS 9. I can see the iframe become larger, the text inside the textarea, and even the button. What effect did you want to have ? The checkbox doesn't grow, that's true, but that's because zooming only enlarges the text-size. Not widgets, images or whatever. It's not a zoom of the entire webpage ! That's bug 4821 ... Do you ming if I duplicate this bug against bug 4821 ?
Ooops. This happens in Mozilla 1.0.1 e Mozilla 1.1. So I guess I have to install the 1.2 alpha 8^). OK, set it as duplicate (or close it altogether).
*** This bug has been marked as a duplicate of 4821 ***