Since extension is sending urls to the backend, it's potentially not secure to do so on websites like banks. While extension supports blacklisting it's not really great to rely on user to do so.

Perhaps some of these lists https://github.com/cbuijs/shallalist would be a good start, unclear how often is it updated though.

Also need to add a UI explanation if the link is blacklisted; and an option to whitelist urls from the 'default' lists in case user really really wants it.