UserAgent: Mozilla/5.0 (X11; Linux x86_64; rv:48.0) Gecko/20100101 Firefox/48.0

Example URL:
https://appear.in/

Steps to reproduce the problem:
1. Travel to China (that's important!)
2. Go to https://appear.in/ or https://room.co/ or https://talky.io/ or any other webrtc video chat that also allows screen sharing
3. Talk with someone else using one of these chats. It works.
4. That other person asks you to share screen. You have never done it before.
5. You click the "share screen" button. It says (it's just a <div>) that you should click "add" to install the extension.

What is the expected behavior?
I should be able to click "add" (and it works outside China, or over an illegal VPN).

What went wrong?
There is nowhere to click "add". So I can't install the extension and can't share my screen.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? No 

Does this work in other browsers? Yes 

Chrome version: 53.0.2785.92 (64-bit)  Channel: n/a
OS Version: Arch
Flash Version: 

Blame Chinese government for their firewall that blocks users from downloading any extensions. Because such governments and firewalls exist, and because Firefox does not require any (impossible-to-download) extensions for screen-sharing, please consider removing the requirement to install an extension. Or maybe, as Firefox did, make sure that popular WebRTC screen-sharing sites are implicitly granted the permission to access the screen. You can take the list from the "media.getusermedia.screensharing.allowed_domains" Firefox preference.