I love your extension, and I have a question regarding the 256x256 ico format.
I have an .ico that was created with another tool (I don't know which), and the 256x256 image is a PNG image (the others are BMP), which saves a lot of spaces inside the .ico
I see that every format is saved as BMP with your tool, even the 256x256 images, so the same ico may be a lot greater because of the BMP format instead of PNG for the 256x256 image.
Couldn't you do something about the 256x256 images, so that they are saved as PNG instead of BMP? (Vista and 7 can only read 256x256 PNG icos I believe)