Browser takes huge part from my screen, take it back to normal!

Hi, this is unbelievable, I did not ask any update, I want my old layout back !! This new version takes a huge place from my screen. Tell me how to make it to disappear and get FULL SCREEN again please !!!

Hi!
it’s not clear to me what you refer to, could you please be some more specific? Anything specific to the developer tools or is that Firefox?
Thanks