This works pretty well.

Some caveats like having to use the tv version of the site in the browser which is understandable due to enabling cast options (you could just have it in a separate tab/window out of the way anyway), the other is that the cast name is Xbox 360, I'm assuming its spoofing the header in your browser so YouTube site thinks it is one. Would be nice to be able to change that but probably not possible.

All in all, this is useful for those that have a pc connected to a nice sound system and the tv is off and you can now cast music videos all from your phone. Nice job.

Edit: Just noticed you have to have the tab active or it just pauses. Is it possible to have it continue working while looking at other tabs?

Edit 2: A workaround for the annoying pausing for now is to have the youtube.tv tab in a new window instead and set this in about:config to false: media.block-autoplay-until-in-foreground

Works as descibed, been using it for 3 days now. Pretty straightforward to set up really, so I'm quite happy with it. People complaining about functionality this extension never claimed to support should read the desciption a bit more extensively.
TY M.K.

thought by this add-on an android phone device can control a TV set which latter based on android as well. what is the point of controlling YT on a computer by your phone? you have mouse and keyboard anyway ...
thank you Mark for your detailed response. so in case of your particular case a(n) (old) TV set is involved indeed. plus you write "... Enables the YouTube for TV interface in your browser .." which can be understood that way that you can control your TV set directly from the browser. i lost couple of hours, so 3-star remains

That thing tells me to find an icon that does not exist. Lost 10 minutes searching everywhere for the legendary icon.

You need youtube TV 😞

Works. Probably shouldn't need to be an add-on, but hey, some people like it I guess. Please list your user-agent.

Unfortunetelly every time I try to use it I get:

"You are being directed to youtube.com"
"For a better experience, check your device’s app store for the official YouTube app."

And I get forcefully redirected to a normal site after a couple of seconds. There's no other button / wheel cog to change anything.
Any ideas?

I thought this was just a web shortcut to the Youtube TV link, but it's also doing something to make Youtube think this is a TV so it actually works

can cast to 4k no problem but noticed that any video that runs 60 fps defaults to 720p. makes some videos unwatchable because of this issue

this addon becomes almost pointless when only having video quality support up to 720p..

I wrote and tested this fix in about:debugging#, this will make all video qualities available
Update background_script.js with this:
"use strict";
if (typeof browser === "undefined") {
var browser = chrome;
}
const targetPage = "https://*.youtube.com/*";

const uaKey = "user-agent";
const refKey = "referer"
const tvUa = "Mozilla/5.0 (PS4; Leanback Shell) Gecko/20100101 Firefox/65.0 LeanbackShell/01.00.01.75 Sony PS4/ (PS4, , no, CH)";
const tvPath = "/tv";

function rewriteUserAgentHeader(e) {
const targetPath = new URL(e.url).pathname;
const originPath = e.originUrl ? new URL(e.originUrl).pathname : undefined;
if (targetPath !== tvPath && originPath !== tvPath) {
return;
}
let uaHeader;
for (let header of e.requestHeaders) {
if (header.name.toLowerCase() === uaKey) {
uaHeader = header;
break;
}
}
if (uaHeader) {
uaHeader.value = tvUa;
}
return { requestHeaders: e.requestHeaders };
}


browser.webRequest.onBeforeSendHeaders.addListener(rewriteUserAgentHeader,
{ urls: [targetPage] },
["blocking", "requestHeaders"]);


**edit**
Well 2k is certainly better than 720p.
You're welcome.