Mozilla's Android components repo describes the project as "A collection of Android libraries to build browsers or browser-like applications." Since this includes an entire browser engine and browser features such as autocomplete and history/bookmark syncing, I don't think this is meant to be a substitute for Chrome Custom Tabs. If you intend to develop a complete browser (e.g. Brave) or an app that uses multiple browser features (e.g. a shopping app with a built-in browser), then Mozilla's Android components might be right for you.
https://github.com/mozilla-mobile/android-components
The Mozilla Reference Browser appears to be targeted to end users as a way to showcase performance improvements in an upcoming version of Firefox. Right now, Mozilla isn't able to include GeckoView into Firefox Nightly because it doesn't support all of the existing browser features.