What do you think is complex?

Not necessarily complex, but the tab switcher etc is built by Firefox, and probably is what tries to load the favicons to display the icon somewhere?

Why the “complex” qualifier? The code responsible for the incorrect favicon URL bug is very simple, and part of the Firefox codebase not WebKit:

https://github.com/mozilla-mobile/firefox-ios/blob/bd589c194...

Firefox on iOS has about 200k lines of Swift. As a rough rule of thumb, everything that isn’t directly related to rendering something within the page or executing JavaScript is Firefox code not WebKit code. So bookmarks, syncing, tabs, etc.