Customizing Chromium to be less alien

Chromium in its initial configuration also feels like a gnome from Mars.

First, make sure that the Chromium installation did not change the default browser:

KDE System Settings > Apps & Windows > Default Applications > Default Applications > Web browser: Firefox

Then, there is a major problem: There is no way to raise/lower the Chromium window.
It's not a problem with the KDE setting. It's a problem caused by Chromium.
The fix:

Settings > Appearance > Use system titlebars and borders: Enable

Other customizations:

Settings > Languages > Spell check > Check for spelling errors: Disable

There's no way to make this browser ad-free. Google prevents that.