I would hate to have a 40px title bar doing nothing except wasting space on my screen. I've been using this layout for years, and I didn't even consider that anyone could have an issue with this until I read your statement.

I'm not saying that you are wrong to disregard it due to your personal preferences, but please consider that this might not be such a horrible design as you make it out to be. Also, you can be certain that you are not the only sane person left - I think it's just that most of them don't show up on boards and forums.

The parent post is overly strongly worded, but I agree with the meat of it: tabs should not be in the title bar of the window. It's worse usability for a space savings that really isn't relevant because it's so small.

Just because it is not doing anything at the moment doesn't mean it doesn't serve an important, necessary purpose. For a windowed application environment to be functional and usable, there needs to be an easy way to drag windows around the screen. When you start moving things into that space, it makes the system harder to use.

A once-simple action which required minimal thought now requires you to parse an arbitrarily populated area of the screen and find a tiny gap within a litany of buttons and controls and carefully drag that part of the window. If you make a slight mistake and click on a tab or button, the unwanted activation of that control (e.g. switching to a new tab) serves to needlessly penalize the user.

This is not just an issue with web browsers now, but seemingly everywhere. It's been a big issue in the macOS Finder for a while now.

At the very least, Firefox still gives me the option to show the native window title bar, which I very much appreciate. It's certainly not the sexiest part of the UI, given the native element clashes a bit with FF's controls, but at least it's usable! This is an issue that could be solved by giving people a choice via a simple toggle... Most often, the option isn't there.

I'm sorry people have downvoted my post here a bit, and I agree it was a bit strongly worded, but I won't apologize for venting some frustration at what I see as the perpetuation of user-hostile design choices like this.