NET:ERR_CERT_COMMON_NAME_INVALID

New user. 

I an unable to access the internet with either Chrome or Firefox ON MY SAMSUNG TABLET.

I get the "setup an Xfininty Gateway" and you will want to download the DXfinity xFI app...but I have already done so!

When I click on Chrome and try to go to a website I get: YOUR CONNECTION IS NOT PRIVATE...attackers might be trying to steal your information from (website),....etc. 

The error message is: NET:ERR_CERT_COMMON_NAME_INVALID.

Aps work fine...but not the browsers. Help please!