While it does work, I found it is being blocked by Facebook for many things, or breaks facebook (firefox). I couldn't see the timeline stream past the visible screen rendered (no scrolling, just grey rectangles forever loading) and chats... this is strange... CTRL+V a link, image data (screen cap to paste) instantly closed the chat window in facebook.com 's messenger pop up window area.

So if you have a use for this keep using it, sure, but facebook is either blocking it or this is blocking facebook. So, use chrome etc for facebook. vice versa. :)

12-02-2022
So in firefox there is an add-on named:
Absolute Enable Right Click & Copy (Force Enable Right Click & Copy) v 1.3.8 updated May 25, 2021

Facebook blocks this and in the opposite direction it messes up pasting screen captures to people in Win10 Win11.
So if you press WIN SHIFT S and copy an area of your screen, usually you can go into messenger
and CTRL + V to paste that from memory into chat.

When this add-on is running (12-04-2022) it breaks that now with either a facebook javascript change on their side, or a firefox change, maybe a change with the add-on. Turn off the add-on and then reload facebook on the browser, and it will allow you to paste screen capture images you don't have to waste the additional step of saving as a jpg or png to your pc first.

good

Works nicely. Still works as of May 2021.

I use its userscript version which work perfectly on Waterfox 56.5

SIIP

It works on websites that doesn't allow you to right click on it, this is what I've been searching for. Thank you!

牛逼。操作简单瞬间解决问题