The Features section on GitHub says it all I think, it basically gives us back app selection on more recent versions of Android and on top of it, it has a lot of optional nifty URL parsing and processing features like Fastforward, ClearURLs, etc. As well as open in private window for Firefox
As a workaround until this is a feature people interested in that could install Firefox Klar and set it as a custom tab provider. It's basically an incognito-only version of Firefox.