My understanding is that on Desktop it's much more difficult than it ideally should be.
With that said we've got a pretty solid story being worked on for mobile via GeckoView [1] and Android Components [2], there's a post on the Mozilla Hacks blog about our use of them in Focus [3] and they're also what is being used for building the "next generation" version of Firefox for Android currently code-named Fenix [4][5].
I wouldn't be surprised if there was an effort to get some of the GeckoView work back onto our desktop platforms.
[1] https://github.com/mozilla/geckoview
[2] https://github.com/mozilla-mobile/android-components
[3] https://hacks.mozilla.org/2018/09/focus-with-geckoview/
