Valmware on safar + Macbook?

Based on what you provided in your post, it may be possible that some form of adware/malware has "infected" his MacBook. I suggest that you try Malwarebytes for Mac to detect and remove any from this notebook.

What you described is how Adware/Malware behaves.

You will need to figure out which Malware is causing the problem and remove it.

It's very easy for anyone to accidentally install Adware when visiting bad web site.

Most of them are very annoying, but otherwise harmless.

Try this link: https://discussions.apple.com/thread/6825026?answerId=27644399022#27644399022

Suggest downloading the Application Etrecheck directly from a well Respected ASC Contributor. 

This application can also be used to identify Malware / Adware

The application is free or paid from added features. 

Run the application with Full Disc Access ( Security & Privacy - Full Disc Access ).

It will take a Snap Shot -  both the hardware and software.

 The Report will Not Reveal Any Personal Information. 

Post back the Full Report - copy and paste - using the Additional Text Icon ( 3rd Icon to last )

We can have a look at the report for possible issues and may have possible suggestions to resolve the issues.