Firefox Quantum (>=57) How to toggle all toolbars? (with a keyboard shortcut, like F11 but in a window, not fullscreen)

This doesn't give you a keyboard shortcut, but you can use the :hover pseudoclass to allow auto-showing the nav box (the toolbars at the top of the browser window) when you hover at the top of the window.

Put this in your userChrome.css:

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");

#navigator-toolbox {
    position: relative;
    z-index: 1;
    height: 3px;
    margin-bottom: -3px;
    overflow: hidden;
    transition-property: height;
    transition-delay: 1s;
    transition-duration: 2s;
}

#navigator-toolbox:hover {
    height: 62px;
    transition-property: height;
    transition-duration: 0.5s;
    transition-delay: 0s;
}

You will also want to tick the "show title bar" box under Customize.

Result: