Set up Chrome as default browser
com.android.chrome with version 69.0.3497.100 has browser.useCustomTab = false

Set up Firefox as default browser
org.mozilla.firefox with version 62.0.3 has browser.useCustomTab = false

Looking at this data in the AuthorizationService constructor by setting a break point and inspecting the browser variable.

Tried to white list Chrome, Firefox and Samsung browser via AppAuthConfiguration but then it just gives activity not found exception in the console and program stops.

Run simple test of
CustomTabsIntent.Builder().build().launchUrl(this, Uri.parse("https://www.cnn.com"))

This runs and uses a custom tab in the app without any issue so custom tabs are usable via code on the device using either browser.

App is built using androidx libraries 1.0.0, Kotlin version 1.2.71, supportLibVersion = '28.0.0'