Thanks. Saved me a whole bunch of time flicking the add-ons on and off. Disabling this Auto Quality for YouTube fixes the issue with all the Discourse based forums I am on. It happened on both Google Chrome and Microsoft Edge (fully updated).
When the add-on is on - You cannot scroll down in forums. Not sure how is the add-on making this happen but CTRL + SHIFT + R seems to be a temporary remedy for those that need the Addon.
Is someone looking into this? What is the addon triggering? Why does it break discourse based sites?