Different browsers handling color profiles differently. The best test to see if the ICC Profile is applied correctly is to save the rendered image with &iccembed=1 and open it in Photoshop. If the color is correct, the ICC Profile is being applied correctly. For example,
Color managed browsers sometimes have to map their own color values to the rendered image. These color values don't necessarily match the ICC Profile. Or, the browser does not provide color management or the color management feature is turned off.
There is no real solution to the end users viewing these rendered images, except to find an output profile that works in most cases. All the modern browsers do provide color management, but you can run into certain ICC Profiles that the browser or operating system cannot map correctly. There is also the scenario where you can color correct your monitor which can provide a different output as well.
This site is a good test site to see the differences for color managed browsers and gives you tests to try out: http://www.gballard.net/psd/go_live_page_profile/embeddedJPEGprofiles.html