They should just put a toggle for it under the Customization page. I think that would be the simplest way to placate peope that dislike it. (Yes I know you can about:config to fix it, but a toggle makes more sense.)
But the problem with the current about:config flag is it's actually changing the entire code pathway, and is going to be removed in a couple months!
[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.
https://windows-cdn.softpedia.com/screenshots/miranda-im_12....
The picture you posted is a positive example. An example on how to customize the software you use.