I can't seem to get it to work. There are a lot of google sites, so I would like e.g. books.google.com to display a book favicon and not the "G."
I opened the page for the extension. Entered https://books.google.com
downloaded and selected a book favicon and saved it as a png file. Now when I type in books.google.com to the address bar the favicon of the tab is changed to the book favicon of my choice but my bookmark bar favicon remains the G even if I drag the new book favicon Google Books tab to the book mark bar.

Additionally, pages that I open with my bookmark bar entry at the same address, do not have their favicon changed, unless I reload them.

I have tried it with another URL and the same result.

I am not using the name string now but I did try it.

I have tried deleting history too.