Favicon is short for “favorite icon,” and refers to the little icon in the address bar of your browser. The favicon also appears on the tab of each browser page. Depending on your theme, a sample favicon may already be uploaded for your store.
Favicons are generally 16x16 pixels or 32x32 pixels in size. Although Magento accepts .ico, .png, .jpg, .jpeg, .apng, and .svg file types, not all browsers support these formats. The safest format to use for a favicon file is an .ico. Many free tools are available online to convert more common image types, such as .png, .gif, and .jpg to the .ico format. Because Magento Go does not convert an image from one format to another, any file conversion should take place before the file is uploaded to your store.