I generally have a "home" Firefox window with my most used tabs pinned. Sometimes I close it before another window, so I was frustrated to "lose" it and having to redo my pins. But recently I discovered this feature. Joy!
Firefox isn’t tracking your bookmarks and selling it to advertisers, Firefox is open source. They keep your bookmark order as convenience so that you can have them in the order you like. Same goes for history, it’s just a tool to see what sites you’ve visited if you’re trying to get back to one, it’s not tracking you.