Comment 4 for bug 175409

I would really love this too. Web favicons are the least important reason for this feature; png is way better. I would use it for creating multi-resolution windows icons for general customization, while others would like it to make icons for their programs and such. Otherwise I'll have to export my svg at various resolutions and open and set them up in Gimp.

A very, VERY neat ability would be if for images that will be in the same form in the icon at every resolution, by exporting, it automatically packages the one target area of the svg to the ico in all the major resolutions (128x, 64x, 48x, 32x, and 16x16).

Anyway, here's a cool guide about how Gimp handles exporting to multi-res icons:
http://egressive.com/creating-a-multi-resolution-favicon-microsoft-windows-icon-file-including-transparency-with-the-gimp