History feels like the only part of Firefox that is still stuck somewhere in the late noughties. They should just copy what Chrome and Safari have done and make it a webpage instead of a separate window.
Slight correction with Safari, it uses a native NSOutlineView rather than a webpage, but the point that history works better in the main browser window stands.
Honestly, I haven't found browser history to be useful anymore. Not in 6 or 7 years. Too many sites are SPAs with server-side state, breaking the back button, breaking multiple open tabs in the same application, or breaking both.
Firefox's visible UI is made of webpages. They just decided to open this webpage in separate window without an option to do otherwise. Still can access it by visiting `chrome://browser/content/places/places.xhtml`.