IF your site is running too slow on IE 8 or IE 9, but it is working perfectly fine on Chrome and Firefox. Check if you are using shadow filter in your css. While Internet Explorer is generally slower than Chrome and Firefox, It is not as slow as when using shadow filters. It really performs terribly that render your site useless and deter visitors from ever daring to visit your site. This is why you should never use filters again. Even scrolling becomes too slow and jumpy. Opening javascript dialog boxes such as jquery lightbox takes extra seconds that it makes the website hard to navigate. While Microsoft describe shadow filter as depreciated on MSDN for IE 9 and above. it is still inexcusable to have it perform this slow especially that IE 8 only supports that way.
The following css makes a huge performance degradation in IE :
filter: progid:DXImageTransform.Microsoft.Shadow(Color=#777777, Strength=2, Direction=0), progid:DXImageTransform.Microsoft.Shadow(Color=#777777, Strength=2, Direction=90), progid:DXImageTransform.Microsoft.Shadow(Color=#777777, Strength=2, Direction=180), progid:DXImageTransform.Microsoft.Shadow(Color=#777777, Strength=2, Direction=270);
Here is a demo of the issue, try this on IE and then on Chrome/Operate/Firefox/Safari. Try to click remove and add filters and notice the difference. Click the images to trigger lightbox and see how slow it is when the filters implemented. Even on simple text page, it is still slow when scrolling. On Chrome and Firefox, the shadow implemented using box-shadow which performs excellently.