I created the Chrome Extension Youtube Fix Ctrl + F because I prefer to use Ctrl + F for finding some text in the page.
The extension stops youtube from going into fullscreen when you press Ctrl+F. Credits to Adrien Pyke for his GreaseMonkey script.
There are no menus involved. Just install and the plugin will take care of the rest.
Tested on Windows.
Comment below if you have issues or want to request something.