Experts say (and I agree) that all images posted to the Web should be sRGB with no ICC profile (the profile is not needed since sRGB is the default on more or less all systems); AFAIK such images should appear the same in different browsers. If you post an image using a low-dynamic-range format (e.g. JPEG) with a non-default colorspace (e.g. AdobeRGB), it will either be displayed wrong (in non-color-managed browsers) or it will lose color accuracy (possibly introducing banding) when the browser converts it to sRGB.
