One feature of Pale Moon that I miss in modern Firefox is that it has excellent support for RSS/Atom feeds.
Modern Firefox does not detect RSS feeds and alert you to their presence. If you click on a link to an RSS feed, you see XML gibberish and no way to subscribe to the feed.
Pale Moon, just like the Firefox of yore, displays a feed icon in the address bar when you arrive on a page with feeds. Clicking this icon will take you directly to the feed, if there is only one, or allow you to select from multiple feeds.