Favicons are used for many things, including browser tabs, bookmark/favorite lists, iPhone/Android home screen icon and Windows tile type home screen icon. To serve all these purposes, we have used a tool at real favicon generator to create about 35 images for various purposes and resolutions.
The smallest image files are used for tabs and bookmark lists. We have used no compression and the best scaling algorithm out of the six on offer to reduce blur. Since using the full letter logo as favicon might be a push, we have made two further candidates for the smallest images to compare: Os (the chemical symbol of Osmium) and a plain O.
Osmium as favicon as well as icon: https://favicon-osmium.abergdesign.uk/
Os as favicon and Osmium as icon: https://favicon-os.abergdesign.uk/
O as favicon and Osmium as icon -this site!