I know that. The whole thing started for me today when I advised a user on some web forum this exact way of bringing it back. Then, out of interest, I dug into the code and the bug tracker, only to find that absolutely nothing was stated about the changes, even though they have been cooking for a month¹. My first real browser was steel-gray Mozilla Suite, back then I opened as many forum topics in tabs as it was possible during a free promotional 5 minute modem connection.
The problem is not inclusion by default, the problem is unwarranted unconditional removal, whether it is default or not, and whether it is needed or not. Mozilla has decided the pretend it happened “by itself”, but it was their decision, and they had an option to switch people to non-sponsored Yandex search.
¹) http://web.archive.org/web/*/https://support.mozilla.org/en-...
https://imgur.com/BVlfEIz
It's also in the right click menu for the address bar.
Why does Mozilla need to include Yandex as a default option?