Lets you replace a bookmark’s icon / favicon. Right click any bookmark, select “Properties”, then “Browse”. (Folder icons aren’t supported yet).

Features:
–> works with many image formats (jpg, gif, png, bmp, etc) as well as .ico files, even animated gifs!
–> any image size can be used, as well as the standard 16×16 pixels (they still display as the small size).
–> grab images from a url – click “Browse” and paste in an address like http://www.cnn.com/favicon.ico
or if a page has an image you like, right click on it and select “Copy image location”, and paste that in (Win only, for now).

If icons are not showing, try the options: (Tools->Add-ons->Favicon Picker->Options) and UNcheck both boxes.