https://www.askvg.com/tip-list-of-all-hidden-secret-internal-pages-and-urls-in-chrome-firefox-and-microsoft-edge/

There are internal local routes inside browsers which are used for debugging purposing by developers but one can find a use case for him selves. Play around with it to find something interesting.

Here are those internal routes/urls corresponding to the browser. Put it in url bar (omnibox/search bar) and hit enter.

chrome - chrome://chrome-urls/ firefox - about:about edge - edge://edge-urls/

I'm pretty sure that most of the browsers have this you can just google like this "[your browser name] internal urls"