I do like that in Thunderbird I can go to settings and search for "Title" to find it. Once I became aware of "Settings", this was easy. In Firefox, this does not work and it took me a while to figure out where it is in Firefox.
I do like that in Thunderbird, I can go to Settings and search for "title" to quickly find this control. Once I became aware of TB's "Settings", this was easy. This does not seem to work in the current Firefox. I ended up spending a long time finding the Firefox checkbox for this. So I do have a slight preference for the TB way of doing this if these were the only two options.
BTW... The reason I want to expose the title bar is that I have several monitors, and Win11 seems to do a poor job of showing me which desktop window across those monitors has focus unless they all have title bars. Only if a window has a title bar will Windows desktop show me which desktop window has focus. If it were not for that, I'd prefer to have no title bar in either FF or TB. And similarly, if FF and TB highlighted itself on Win11 when it has focus, I would not want to expose the title bar of either.