Works as described. Nice job!

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.

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

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.