Favicons for your Nimbus website are kind of persnickety, so if you are trying to upload one and are running into problems, check the below list of requirements to see if what you are uploading meets them.
- It must be square: 16x16, 32x32, 48x48, or 64x64 pixels in size.
- Color depth cannot be higher than 32-bit.
- Modern browsers support JPG, PNG, and GIF, however Internet Explorer supports only the ICO format.
- Many tools are available online for creating or converting to ICO files. Google for "ICO" or "favicon" if you need help finding tools.
- Atrium does not support animated GIF favicons.
More info here: http://en.wikipedia.org/wiki/Favicon#Browser_implementation