This is a Firefox add-on to make it easier to use tablets with the browser in full-screen mode
It adds three on-screen buttons: Close, Back, and Full-Screen.
The big thing is that you now have an easy way to close tabs and to toggle between full-screen and normal view even if the toolbar or address bar aren't visible and you don't have a keyboard or it isn't connected. These buttons are shown on all web pages, and try to be quite non-obtrusive (but may not always succeed.)
Another thing that can be annoying is that it may take a while for the buttons to show up, and sometimes they may not show up at all or may be hidden by other UI elements. And there's at least a site where the icons are not shown (though the buttons still work.)
Although it seems to make sense to allow some customization (button color, size, placement), there is currently no support for customizations, but it may be added if there's a real need.
Download the sources, go to about:debugging in Firefox, enable add-on debugging, click on Load Temporary Add-on, pick a file from the project (e.g. the manifest.) Now the add-on should be installed and non-Mozilla sites should have the 3 buttons in the upper-right corner.