Great, thanks! I renamed the web data file and the search engines are back.
Can I ask you what this file contains? Because the old file was 393kb, and the new is only 8kb.

Hi there!

I'm using the latest stable release version 23.0.1522.60. One day to the next all the search engines disappeared, so I can't search anything up in Google from the omnibar because it does not work. In fact, it automatically jumps to the first relevant URL from the history. For instance, if I try to search for Facebook, it opens my most visited Facebook group instead of Google-searching "facebook". And no, facebook was not auto-completed with the rest of the url! How can I get back the search engines?
By the way, the Google search bar on the speed dial also became very small.

Search engine list: https://p1.picsto.re/searchengine.PNG
Speed dial search bar: https://p1.picsto.re/nULKF.png

Installed extensions: AdBlock, Ghostery, Gmail Notifier, Pocket, Smart RSS, RSS Detector, Violent Monkey