Works flawlessly for me! (as of Feb 2019, FF 65.0)
I don't get what some of the other reviews are complaining about, because I'm really glad to finally have true fullscreen again in Firefox.
One limitation is indeed that you can't change the keyboard shortcut in the addon settings, but I solved it by using an external tool (Karabiner), mapped the standard cmd-shift-f to the addon's ctrl-shift-f shortcut.
Summary: Get this addon if you want real fullscreen back! And, thanks a lot Trishul for this addon.
Doesn't work on Flash game sites that have input bar focused —so it's useless like the userChrome.css trick. Make the full screen trigger without window focus. Nevermind, it's a glitch in Habbo site, I'am back to using this userChrome script: https://www.userchrome.org/what-is-userchrome-css.html
Superb. Works a treat and it does it quickly and looks absolutely perfect. Pressing ESC gets me back to the normal browser view, which is intuitive. There are many times, particularly, when I am writing or designing, that I like to go into total full screen mode (i.e. without the tabs and all the other clutter) and this does exactly that and does it more elegantly than anything else I have come across. Thank you for clearing up my screen so well :-)
A great add-on but for one important issue: the full-screen that is shown is a scaling up of the original downsized page and it's not possible to see the page as it would be rendered in true full screen. If you try to refresh the page to see how it would look in true full-screen the page reverts back to the downsized version. I hope this makes sense. This plugin acts the same as if you were to pull the browser larger instead of loading it initialized as full-screen to begin with. Some backgrounds on pages slide up to reveal empty black or white space beneath because of the scaling up of the view port mechanism. It might sound complicated but for instance with my website in the past I would go full screen and then refresh the page to make sure everything was loading correctly.
As of 15 January 2018, this is the only add-on that will allow fullscreen functionality with no menu/nav bars on OSX 10.12.6 (FF 57.0.4). The browser.fullscreen.autohide function is broken for this machine configuration.
Feature request for this add-on: please add an icon that can be added to the menu bar that does the CTRL+SHIFT+F shortcut with one click.
It works (mostly) as intended. Four things to note: 1. control+shift+F is the keyboard shortcut, even on a Mac. This is actually very helpful. Since it does not override the default fullscreen behavior, both fullscreen modes are within reach (command+shift+F calls for the default fullscreen behavior). 2. Due to some restrictions it does not work on addons.mozilla.org. This might lead to some false reports saying it does not work. 3. As soon as you do anything in a webpage (click a link, search with Google, etc.), it will revert back to the default fullscreen behavior. 4. It requires access to "all data in all websites", so regular code audits might be needed to ensure that it does not do anything malicious.