The eXo Favicon ( ) is packaged in platform-extension webapp: platform-extension.war!/favicon.ico.

You can override it by packaging it in your extension, for example custom-extension.war!/favicon.ico. Note for well display the icon should be 16x16 (pixel).

For a quick test you can download an icon somewhere, like the Google favicon ( ) that can be downloaded from http://google.co.uk/favicon.ico. Resize it to 16x16 and pack it in the extension.

After deploying your extension, you should remove images cache in the browser and refresh the eXo page. Here is the illustration with Google favicon replacing eXo favicon: