Prevent apps opening links in Chrome Custom Tabs (i.e. open in default browser directly)
The Custom Tabs help page says:

What happens if the user doesn’t have a recent version of Chrome installed?
Custom Tabs uses an ACTION_VIEW Intent with key Extras to customize the UI. This means that by default the page willopen in the system browser, or the user's default browser.
If the user has Chrome installed and it is the default browser, it will automatically pick up the EXTRAS and present a customized UI. It is also possible for another browser to use the Intent extras to provide a similar customized interface.

That means, if you make some other browser the default one (this can be done via Settings &gt; Apps &gt; Cog menu &gt; Default Apps), any app trying to open a Custom Tab will open the link in that browser instead.
Update: That also means, it's possible to write a &quot;manager&quot; app that presents itself as a browser (handles ACTION_VIEW intent), and on receiving this intent checks whether it has Custom Tabs-related EXTRAS, and depending on some logic opens a browser of your choice using an explicit intent (where the desired app package name is explicitly specified).