How do I get mozilla firefox to display bookmarks on my toolbar with an icon related to the marked website instead of a blank page icon?

My Firefox used to display the icons of the bookmarked pages on the toolbar with an icon relating to what the website was automatically (for example, “Fluther” would be that little jelly fish guy icon beside the URL bar at the top). It now has stopped doing this and all my new bookmarked pages are the blank page icon.

How can I fix this?