There appears to be an issue in Firefox v2.0.0.8 and the width/height() methods.

If you call them on an element which is hidden and the user is typing in a textarea box, then the cursor jumps to the end of the textarea box.

This does not happen with the css() method.

I've prepared a page that demonstrates the behavior:

http://www.pengoworks.com/workshop/jquery/jquery_height_issue.htm

If you make the hidden div visible, it works as expected. If you use the css() method it works as expected.

Some more digging, it appears the problem only exists when the hidden element is a child of the body tag.

I've tracked the problem down to the jQuery.css function. If you change the lines:

if ( parPos == "static" )

e.parentNode.style.position = "relative";

to:

if ( parPos == "static" && e.parentNode.tagName != "BODY" )

e.parentNode.style.position = "relative";

This seems to resolve the problem. Apparently changing the position of the BODY tag in FF causes some kind of document reset.