A favicon is a convention for websites to provide an icon for browsers to display in bookmarks, favorites, history, and other places they show or list URLs.
You can get favicons for most sites as PNGs using Google's cache of them, e.g.:
- from https://plus.google.com/_/favicon?domain=twitter.com&.png
- from https://plus.google.com/_/favicon?domain=facebook.com&.png
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