Firefox 12 renders the image below in paler colors while Chrome 19, Opera 11, Safari 5 and IE9 render it correctly.
The image on the left is original PNG uploaded to Stackoverflow while the one on the right is screenshot snippet of Firefox’s rendering:


When you view this question page on Firefox you still see a difference. I believe Firefox applies the same color transformation to it’s own rendering (saved by snip tool) too. But I don’t see any rendering difference on stackoverflow logo.
I tried with both Paint.NET’s saved PNG and output of OptiPNG, results are the same. Any troubleshooting hints are also appreciated.
The png image has a gAMA chunk, so its rendering will depend on whether the thing doing the rendering supports gamma correction for PNGs.
Firefox does support this. Other browsers may not.