I majored in CS and I had no idea that was possible: public websites you access have access to your local network. I have to take time to process this. Beside what is suggested in the post, are there any ways to limit this abusive access?
There are no mechanisms in browsers yet. Best you can do is using the OS to forbid your whole browser to access your local network. (And use another browser only for your local network.) Ask ChatGPT for methods to sandbox your browser.