- Open the Bookmark Manager and export your bookmarks;
- Open the exported html file in your favorite editor and look for the bookmarklet you want a favicon applied to;
- Convert the 16x16 px (or greater) favicon you want to use into the BASE64 format (I used Base64 Image Encoder);
- Now you can add the favicon via adding the
ICON="data:image/insert-your-base64-image-code-here"attribute in the link; - Save the file and import it in the bookmark manager.
Done!