Maximize Button missing

I am working on a site which was devloped on sharepoint 2010 but now migrated to sharepoint 2013.The maximize button was working while opening the list in 2010 site,but its not working on 2013 site.I implemented the following function but it just gives the form in maximized state,maximize button is still missing. function maximizeWindow() { var currentDialog = SP.UI.ModalDialog.get_childDialog(); if (currentDialog != null && !currentDialog.$Q_0) { currentDialog.$1Y_0(); } } ExecuteOrDelayUntilScriptLoaded(maximizeWindow, 'sp.ui.dialog.js');

I m working on internet explorer 8.

Wat could be the changes i need to make?