Rogue insertion in my Bookmarks Bar

I have been using Brave browser on a Mac for about 8 months now and am very happy with its general performance.
However, when I opened Brave today, I noticed that a short-term Loans company (aka ‘Shark’) had somehow created a Bookmark in the first position of my bookmarks bar! The website is www.boutell.co.uk. I have never visited this site nor had I heard of the company. These companies are largely discredited in the U.K. and could not imaginably have a relationship with a browser company. How can they interfere with a secure browser in this way?