Honestly I don't even try to read pages that have some super narrow 400px layout any more. Time was I would screw around editing the CSS with dev tools, but I just don't have the patience these days. It's a lot of work to try to alter the CSS and it's unpleasant as heck to read something that narrow (anything less than 1000px is awful to read and I prefer 1200), so I just move on.

Pro tip for web designers out there: if someone wants a narrow layout they can always make their browser window smaller, but if you force it to be narrow that screws over the users who find that unpleasant. A wider layout can thus work for both types of reader, while a narrow layout only works for one.