browser.urlbar.update1 set to false will disable
it, but that option is being removed in FireFox 77.
[0] https://www.ghacks.net/2020/04/08/how-to-restore-the-old-fir...
For me, the bigger address bar is just as bad as an advertisement: it's trying to steal my attention, except in this case no one else is benefiting from doing so.
If they remove the option, I hope someone smarter than me can come-up with an add-on to fix it.
Furthermore, Firefox extensions don't have the capability to mess with the address bar.
Awful. As soon as it can't be turned off, that's the moment I'll finally stop using the browser.
It breaks absolutely "normal" expectations of a GUI.