Remove the address bar padding in Firefox 77

Since Firefox 75, the address bar now looks like this:


It's quite jarring and a waste of screen space for me. This tip will restore it back to how it use to look:


Use this website to customise how the "mega bar" is presented:

After changing the options to the desired preference (in particular, 0 pixel padding), save or append the generated userChrome.css to this file:


(It's a hidden folder in your home directory, press CTRL+H to reveal it)

You may need to navigate to about:config in your browser, and set this key to true:


Then restart the browser.