In https://gitlab.torproject.org/tpo/applications/tor-browser/-/issues/44030 we want to add a destructive styling to one of the prompt buttons. Moreover, the new identity dialog also needs a destructive styling for the button. Rather than create a custom `xhtml` for these cases, we should just modify the `nsIPrompt` and `commonDialog` code to enable the features we want. Some of this could be upstreamed, if mozilla has a used for it: [bugzilla bug 1979020](https://bugzilla.mozilla.org/show_bug.cgi?id=1979020).