The reason thickbox is messing up in IE9 is it is doing a test for IE6 that IE9 doesn't process correctly.
Since IE6 is so old, I figure the best thing to do is just remove this test as it is no longer needed. Look for the following lines around line number 283. (Yours may be different as I have modified my thickbox code a bit, but it will be very close!)
if ( !(jQuery.browser.msie && typeof XMLHttpRequest == 'function')) { // take away IE6
$("#TB_window").css({marginTop: '-' + parseInt((TB_HEIGHT / 2),10) + 'px'});
}
Take away the first and third lines of this bunch leaving you with the following line:
$("#TB_window").css({marginTop: '-' + parseInt((TB_HEIGHT / 2),10) + 'px'});
The if statement first checks to see if you are using IE. If you are, it checks the typeof XMLHttpRequest to see if the version of IE can handle XML - which IE6 can not. It would return false to the second part of the test and not allow the marginTop to be changed.
IE9 returns true for the first test as all IE browsers do, but it also returns true to the second test the same as IE7 and IE8, but still doesn't allow the change to marginTop to execute. Why? I don't know. The fix is to remove the test altogether. If someone is STILL using IE6, they REALLY need to upgrade.
If you want to keep this check in, modify it to use a different way to check for IE6. How you do is up to you.
I hope that this helps you guys out! I registered just to post this for you!
So the default Opencart template is showing the issue, as well as my shop...
