New answers tagged png
As Alex Blackwood pointed out in the comment above, it sounds as if your PNGs are using Index color. When ever you resize with this color mode, the colors get out of alignment and you get noise. What you need to do before attempting to resize is go to Image > Mode > RGB Color
Aside from the comments suggested above, make sure you did not export the image with a "Matte" colour. Leave the field empty and try saving the file again.
There is a difference between how the transparency of the various PNG versions semi-transparent pixels are handled. If you resize and save the PNG to a different version than the original I guess it is possible that the semi transparent pixels were handled differently (ie matte) resulting in the difference you see. I'm not super conversant in any of this but ...
I am not sure if/how browsers scale large icons, but The W3C suggests the following1: The format for the image you have chosen must be 16x16 pixels or 32x32 pixels, using either 8-bit or 24-bit colors. The format of the image must be one of PNG (a W3C standard), GIF, or ICO. 1 w3c.org: How to Add a Favicon to your Site (Draft in development).
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