Right. What I see in that last screencap is “scale to fit”, as in, it has transformed the layout to fit a vertical mobile screen - it has changed compared to your previous “FF at 200% scaling” image (look at the keyboard and textbox for instance). All the FF elements are now present. But this isn’t what you are looking for. You seem to be looking for them to be smaller and fit even more stuff there - “to fit” doesn’t do that. This is the part that Guido missed, if I understood correctly.
I’d approach this for a different direction. I’d like to have the Display scale factor to be actually usable (I’d prefer to use 150% or 175% with L5) but then A) it would have to be persistent, and B) not effect keyboard/squeekboard and the top menu.
There were similar discussions a few years back: Librem 5 scale-to-fit? and Tutorial: Create Shortcuts to Scale Display Up/Down The wlr-randr mentioned in the latter seems promising but I have no idea if it’s still usable. Do you still use scaling @amarok?