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This is a typical usecase for Addons. Not everything should be integrated into a browser. Check out leechblock
I tried Leechblock (Android Version) but it doesn't work. It cannot block web domains.
Why not integrate every possible thing into a browser. Everyone customises and uses their browser diffrently.
The desktop version has all the necessary extensions and why not Android version too. Android doesn't mean smartphones only, it includes Tablets too.
That's just my 2 cents on this.