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.
When you view the feed, instead of gobbledygook you see a pleasantly designed human-readable preview of what the feed might look like in a feed reader. There is an option to subscribe to the feed either within Pale Moon (with Live Bookmarks) or with an external program.
I believe that Firefox eliminating first-class support for RSS/Atom was a blow to the open web, one of many small steps that resulted in the walled gardens of today. It is a trend that we must reverse, and we need universal support for open standards like RSS/Atom and ActivityPub
For anyone intrigued by Pale Moon, I must reiterate that it is a hobbyist project that cannot be considered secure by modern standards. The insane complexity of the modern web cannot be navigated safely without the support of large orgs like Google, Apple, and (for now) Mozilla.
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.