To describe my use case a little bit better, In Firefox I create bookmarks with very short names (like aliases on the terminal), then I can quickly type a bookmark name and press enter without even looking at the results. So this is currently not like a search for more, but more like Spotlight on macOS (but not to open applications, but to open bookmarks in the browser real quickly).
I actually don't need a feature to search only for sites in my history or reading list from the search bar, because I search for those so rarely, but maybe other users do.
But accessing bookmarks in the search bar like apps in Spotlight is really essential in my daily usage of my browser.