Popups break the browser paradigm
Dialogs such as accepting a certificate or allowing some data being sent must be done in browser forms.
Lets take a look at how two leading browsers handle a 404 and a domain which doesn’t exist.
It does the errors within the browser. No popups. Great.
BUT it could be improved. They are inconsistent. And the 404 page provided by the browser could included a feedback form so a user could easily give feedback to the site maintainer.
Wrong, wrong, wrong! What an unhelpful default 404. That screenshot shows the confusion. Is it a 404 now, or does the domain not exist?
On my Nokia’s user agent, the error ”STOP page can not be loaded” just flashes for a second and disapears. Hardly enough time to take it in. Can’t go back to it as it’s a popup. And after comprehending the error, the error does not have any useful information whatsoever to debug the problem.