This is hardly new...

https://lifehacker.com/how-to-navigate-away-from-a-website-t...

I've always gotten around it by Long pressing the Back button and then selecting the page to go to. Bypassed your "block" as well...

This is not a big of a find that you think there is. And I'm not sure calling it a "Zero Day" is appropriate either as it doesn't exactly cause much of a problem.

That is a good workaround.

In Chrome/Safari, this specific bug doesn't exist.

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I don't think this is a "big" zero day. But if non-working navigation results in someone getting scammed then it might be big for them.

Also does not work with uBlockOrigin disabling javascript (either of uBlockOrigin's global block or inline script block prevents it from working).

Right click on the back button will show you a list with the previous pages. Looks like it doesn’t affect it.

This is not a zero day, disabling the back button is a commonly employed technique on some sites.

And each of them are a vulnerability.

This one here is not affected in Chrome

You can't use the back button to leave a page