Padding still gets in my way on a 38" ultrawide with two 24" monitors next to it, because my poor (uncorrectable) vision requires substantial UI scaling.
If you can use tiny fonts for everything else I'm sure the padding is less painful but it's super annoying if you have to scale things up and you can actually get completely lost in it if you have to use much fullscreen magnification.
This would be less frustrating if I could easily scale up UI fonts without also scaling up the whole UI proportionally, along with the padding.
In terms of apps in my life with annoying padding or wasteful use of screen real estate, though, I have to say Firefox doesn't even remotely make the list.
