You can access the main menu by pressing a-b even from the root folder. You don't *need* to use "left", but you can. Slight but for some an effective difference. The initial main menu didn't had this shortcut but most users want it (and unfortunately not too much voted against it, so it got added).
You can of course simply remove the key binding that backs out from the browser to the menu. Which of course requires creating a build of your own ... (but, while I dislike the backing out from the tree views to the menu, I simply just use the menu button, so it's not a big deal for me)