I think is what is happening is it has something to do with how the Fieldset width is interpreted in the standards based browsers. It appears that even though one would think that the table width alone would constrain the width attribute of everything inside, it apparently does not hold true for the fieldset attribute.
Because it looks like there was no defined width, the fieldset just fills out 100% minus the padding and margins that were applied or inherited. In Safari's CSS editor, I was able to apply an inline style that fixed the form issue to this element: <fieldset class="Cool_Default" id="Contact_me">
You could easily add the inline style like this to it:
<fieldset class="Cool_Default" id="Contact_me" style="width: 490px">
This wouldn't be my most desired way to fix this problem every time because if you had to re-enter the form builder to make edits, I believe this inline style would get over-written. But, this would be a quick way to fix it right now if you are in a hurry.
The other thing to try would be to style the element within form builder - selecting the fieldset attribute and setting it to the fixed width of 490.