On Mac 10.6.4, I see that Webkit supports ICC V4, but Firefox 4 does not. Obviously, we should always tag with V2.<p>What I don't understand is the final test: comparing an sRGB tagged image vs. an untagged image. No current browser on a Mac is assuming sRGB as a default? That's just crazy! I did check the source images, and they are correct: same formulas. One tagged sRGB, the other untagged.<p>I often have relied upon the sRGB default to keep my image filesize down. No longer. I'm tagging everything from now on. We've been able to coast in the past, because most displays have a gamut smaller than sRGB. Not true anymore. Modern LED-backed LCD panels generally exceed sRGB gamut - meaning your images will have an improperly extended gamut if you don't tag them.