Fix JS hooks on really slow connections

[aaronpk]

When the HTML of the page loads super slow, the JS for interactions like marking as read or favoriting attaches too slowly. The HTML of the page hasn't finished downloaded yet but the browser still starts rendering content.

I need a way to start attaching events to DOM elements as soon as they appear in the document rather than waiting for the full document to be rendered.

Possible things to look into: intersection observer, mutation observer.