Improve sidebar hiding threshold on portrait screens

I always use my browser (Firefox, cuttently 76.0.1) on a 1280 x 1024 screen in portrait mode, and the layout seems to automatically select the mobile version for that. Which is really inconvenient, since the navigation bar is automatically hid every time I click on an index entry, and you have to always click on the hamburger menu between switching subsubsections.

Also, it is not really indicated in any way that not hiding it is even possible -- I only today had the idea to try resizing the window.

Could you maybe restore a threshold closer to the one in the old layout, where the navigation bar always stayed (1055 px is just a tad too much for my screen)? Or at least give an option to "pin" the menu on desktop screens?