How to Hide WHO Covid-19 Banner on YouTube

Based on the extension as posted by @phwd, I've created a simple script that is designed to do exactly one thing: remove in-video advertisements.

Simple installation instructions for Firefox

1. Go to https://addons.mozilla.org/firefox/addon/greasemonkey/ and press the green installation button
2. After installation of the add-on, restart Firefox
3. Open http://lekensteyn.nl/files/Remove_in-video_Youtube_adverts.user.js and press the Install button.
4. Profit!

Other browsers

Instructions for installing this script across various browsers can be found on https://stackapps.com/tags/script/info

Firefox with Noscript

If you're using Firefox and have NoScript installed, you can use the below surrogates. You have to add two settings to about:config, both of type string.

1. Key: noscript.surrogate.removeVideoAdsYoutube.sources
   Value:

   !@*.youtube.com

2. Key: noscript.surrogate.removeVideoAdsYoutube.replacement
   Value:

   (function(){try{var o=ytplayer.config.args,i;for(i in o){if(o.hasOwnProperty(i)&&/^(afv_)?ad/.test(i))delete o[i]}}catch(e){}var a=document.getElementById("movie_player");if(a){var b=a.cloneNode(!0); b.setAttribute("flashvars", a.getAttribute("flashvars").replace(/&(afv_)?ad[^&]+/g,"")); a.parentNode.replaceChild(b,a)}})()

If you want to make your own surrogates, have a look at http://hackademix.net/2011/09/29/script-surrogates-quick-reference/

UPDATE (02/24/14): fixed noscript surrogate code. Greasemonkey script still broken at this date.

You could use a DOM editor (Chrome has one built in) and delete the element. Unsure if this stops "streaming" though.