Safari/Browsers - Eliminating browser redirects and advertisements
See if the same thing happens in the Safe Mode.
Safe Mode - About
If it works in the Safe Mode, try running this program when booted normally and then copy and paste the output in a reply. The program was created by Etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. Click “Share Report” button in the toolbar, select “Copy to Clipboard” and then paste into a reply. This will show what is running on your computer. No personal information is shown.
Etrecheck – System Information
If the log won’t post, try posting it in Pastebin and provide a link in a reply Pastebin