How Can I Hide All Toolbars When Firefox is in Fullscreen?

I want to use firefox as a front-end for users to see only one website.

I found how to start firefox in fullscreen, toolbars are hiding by default, but I cannot make the toolbars (address bar, tabbars etc) not showing up when the user hovers on the top of the screen.

Is there a way to do this?

As lexu mentioned, what you want is typically called "kiosk mode". To my knowledge, Firefox does not include built-in kiosk mode functionality (I think only IE includes it in the base version), but it is available with a couple of different Firefox plugins.

R-Kiosk is perhaps the most popular one. I've used it before in one of my previous jobs with a Firefox 3.x setup, but I haven't tried it in a couple of years so I don't know about compatibility and functionality with newer browsers. It does state it works through the latest versions of Firefox.

The other fairly popular one is FF Fullscreen which I haven't tried, but doesn't appear to be a full kiosk mode that prevents users from getting to the desktop, but rather just a fullscreen with no toolbars mode, which might be what you're looking for anyway. Your question didn't state whether or not you wanted to keep users from getting to the desktop.

You can advantage of HTML5 Full Screen API.

Paste code below into console and click big black box to activate fullscreen mode:

(function() {
  var el = document.createElement('div'),
      docEl = document.documentElement;

  el.innerText = 'Go to fullscreen view';
  el.setAttribute('style', 'position: fixed; top: 10%; left: 10%; padding: 30%; background: #000; color: #fff; opacity: .7; cursor: pointer;')
  document.body.appendChild(el)

  el.onclick = function() {
    if (docEl.requestFullscreen) {
      docEl.requestFullscreen();
    } else if (docEl.mozRequestFullScreen) {
      docEl.mozRequestFullScreen();
    } else if (docEl.webkitRequestFullscreen) {
      docEl.webkitRequestFullscreen();
    }
    document.body.removeChild(el);
  };
})();

...or use bookmarklet:

javascript:(function(){var e=document.createElement("div"),t=document.documentElement;e.innerText="Go to fullscreen view";e.setAttribute("style","position: fixed; top: 10%; left: 10%; padding: 30%; background: #000; color: #fff; opacity: .7; cursor: pointer;");document.body.appendChild(e);e.onclick=function(){if(t.requestFullscreen){t.requestFullscreen()}else if(t.mozRequestFullScreen){t.mozRequestFullScreen()}else if(t.webkitRequestFullscreen){t.webkitRequestFullscreen()}document.body.removeChild(e)}})();

Got to about:config , search for browser.fullscreen.autohide and change the value to true.

Possible values and their effects

True

Automatically collapse toolbars and the tab strip in fullscreen mode and only show on mouseover. (Default)

False

Always show the toolbars and tab strip in fullscreen mode.