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.

Google Docs is using the same shortcut. Could you consider adding an option to change the shortcut? Thanks!

For some reason it didn't work until I restarted Firefox, but now it works flawlessly. I use this add-on to remove distractions so I can concentrate on my work. Thank you whoever built this!

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 :-)

UPDATE 2021-08-22:
Les Merlotta's trick for Mac from 2020-10 is still working on Firefox 91.0.1 Mac:
"Type "about:config" in your Firefox address bar (like going to a website), click "Accept the risk and continue". Then copy/ paste "full-screen-api.allow-trusted-requests-only" and change it to false."

OLDER COMMENT:
Thank you Trishul, good job. Running fine in macOS 10.10.13 High Sierra with Ctrl+Shift+F. I like that Cmd+Shift+F remains for the default full-screen behavior.

Just one request: please add an option page where to toggle if FS mode shall be left or kept when clicking onto a link (and maybe another option when leaving a domain).

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.