Firefox on desktop does not have this; also its not related to search engines, these lists of domains are embedded into firefox.

Where’s the source code for Fennec? The link on its f-droid page is just firefox-android repo.

upd: found it https://gitlab.com/relan/fennecbuild

Drew Devault has his own peertube on spacepub.space. Look for example at him coding in a VR headset or on a typewriter.