Change favicon file format
The current favicon for the project (the little picture in your browser tab when you load the site) for this project is in the .ico format. The use of this extension derives from this project's original support, back in the day for IE 6. Even vaguely more modern browsers use .png files instead, and for good reason: .png files cleanly scale, rather than requiring an icon rendered at various specific resolutions (16x16, 32x32, etc).
File to change located at srctweb/_includes/head.html
Note that the og tags are already using .png images for the link expansion.