YouTube Theatre view by default without extensions

Go to https://www.youtube.com
Open dev tools of the browser you are using (Press F12 or Right-click -> Inspect)
Select Console tab
Paste below code and Enter:

document.cookie = 'wide=1; expires='+new Date('3099').toUTCString()+'; path=/';

Thanks

grub2 can remember last choice

Put the following in /etc/default/grub

GRUB_DEFAULT=saved
GRUB_SAVEDEFAULT=true

Then run:
update-grub

Thanks