Cannot shut down Safari on my Mac Book?

Safari doesn’t stay quit?

Adware is installed on your Mac.

     Use  the latest release of MalwareBytes for Mac to remove malware/adware.

     Install guide:       https://support.malwarebytes.com/docs/DOC-1817

     Uninstall Guide:  https://support.malwarebytes.com/docs/DOC-1190

     The installer may ask you to allow it in Security & Privacy  /System Preference. Allow it.

     Click the “Scan Now” button. Once done quit Malwarebytes for Mac.

     Restart the computer, relaunch Safari holding the shift key down.

1. Backup your Mac.
2. Try Disk Repair. Repair a disk using Disk Utility on Mac - Apple Support

3   If this doesn't help,   download EtreCheck: https://etrecheck.com/maspro  and post the report here.

      Click, “Free Download” button and then  “Click to download” button,

      open Downloads folder, click on it to open, and then select ”Open”.

      Click on the bouncing  EtreCheck icon in the Dock.

      “Choose a problem” from the popup menu box, and then “Start EtreCheck” in the dialog.

      Click “Share Report” button in the toolbar, select “Copy report” .

      Paste the report when you reply.

      Note: This is a diagnostic test. Reading the report will help us not make unnecessary suggestions.

You may have to run Malwarebytes repeatedly two or three times.

Few users have reported that repeat scanning helped them.