To change the icon that is displayed on the bookmark in a browser from the:
To something more sexy, then do the following:
Create a new folder in this location C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\IMAGES
I named my folder “Custom”. This is always best practice, so that your changes wont be overwritten in any update.
Paste your new favicon file. Don’t forget to rename the file extension to .ico or it will not work.
Open the html version of your custom master page (if you don’t have a custom master page, add one)
Find and change the path inside the tag SharePoint:SPShortcutIcon