How to get favicon for a tab in JS for an Extension?

Add-ons Development
#1

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:88.0) Gecko/20100101 Firefox/88.0

Steps to reproduce:

OneTab uses a google service to get favicons and https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIFaviconService is deprecated, Is there a modern way to get the favicon for visited sites/open tabs?

#2

Tabs for example give you the favIconUrl. There is no way to access the cached representation as of now.