Resize iframe height dynamically

My website currently uses two iframes in the left menu navigation bar. Their heights are too large so I cannot fit anything else there but those two. I want them started out collapsed at a defined height (~ 250 px) when the page is loaded. Then I want to give user option to expand (by clicking on + sign). When + sign is clicked, iframe should expand. Then, + sign should change to - sign and use can click on it to collapse back to previous height. I have looked all the previous questions but did not find exact solution I need. Could you help? Suggested solution should work in IE, Netscape and Firefox browsers.