Avast Secure Browser

The Avast Secure Browser opens every time I start my machine and sets itself as the default browser.

I go to the settings and remove those settings and on the next boot, it opens again and changes them back.

How do I fix this?

https://forum.avast.com/index.php?board=78.0

Similar thread may offer a solution:
https://forum.avast.com/index.php?topic=235407.0