The problem#
Web browser UIs have a lot more than just displaying the web page, which is useful when using them as a browser, but clutters the screen if all we want is to define what is displayed on part of the screen using HTML. So, can we get Firefox into a mode where it really does show just the website and nothing else? Firefox does have a fullscreen mode that does that, but it covers an entire monitor.
The solution#
To hide all of the Firefox menus and toolbars, put the following
in the chrome/userChrome.css file under your Firefox profile
directory (you will likely want to create a separate
profile from the one you use for web browsing):
#TabsToolbar, #TabsToolbar-customization-target,
#nav-bar, #urlbar-container, #searchbar {
visibility: collapse !important;
}
To hide the window border and titlebar, compile
toggle-decorations.c and run
firefox &
./toggle-decorations $(xdotool selectwindow)
and then click on the Firefox window once it opens. It may be easier to
bind it to a hotkey with xdotool getactivewindow or
use some other way to identify the window.