Last week, I linked to a critique of Google's new "confidential mode" for Gmail and Google Docs, which purports to allow you to send people documents without letting them print, copy or forward them.
It's an old and frankly foolish idea, one that creates an anticompetitive advantage for Google (technologies like "confidential mode" are protected by the US Digital Millennium Copyright Act, making it a potential felony for Google competitors to create products that connect with them) without providing any real security for Google users (if you send someone an email, they can just take a picture of their screen).
But when it comes to defeating confidential mode, there are even more effective, easier ways to break the restrictions on emails and attachments: Firefox's "Style Editor" lets you tick a few boxes to disable the restrictions.
It's more evidence that "confidential mode" is a fool's errand. As with other forms of Digital Rights Management (like the restrictions on saving Netflix videos or refilling your inkjet cartridges), confidential mode seeks to provide untrusted parties with sensitive information, and then recruits their devices to enforce limits on how they use that information.
The key here is "their devices." For DRM to work, your devices have to be subverted to act against your interests, to serve remote masters who set policy on them that you can't rescind or countermand. This is a fundamentally absurd proposition. Your devices belong to you, and any legal or technical system for restricting how you configure them is an affront to your most basic rights to use your stuff the way you see fit.
Also: it doesn't work very well. You possess your devices and (inevitably) you can wrest control over them back from distant usurpers. When that happens, the "security" of the system (that is, preventing you from frustrating someone else's wishes) collapses.
But once we give legitimacy to the proposition that you should be able to tell someone a secret but without the risk of their spilling the beans to someone else (a proposition akin to being able to immerse yourself in water without getting wet), we set in motion a train of ever-more-restrictive measures to find a way to approximate the impossible.
The technique of using Firefox to bypass "confidential mode" is possible because Google doesn't control Firefox. But they do control Chrome, so they could configure Chrome so that it turns off the feature that allows you to override "confidential mode" and then turn off Gmail and Google Docs access for Firefox — not in the name of preventing competition, of course, but just in the name of "protecting user privacy."
At the same time, Google could invoke the Digital Millennium Copyright Act's Section 1201, which prohibits "circumvention of access controls" and makes their trafficking a felony punishable by five years in prison and a $500,000 fine (for a first offense!), wielding it as a club to force Mozilla to remove features from Firefox to match Chrome — they could also use this weapon to shut down free/open source software patches that restored the functionality to Chromium (the free/open Chrome) and Firefox.
It's unequivocally true that privacy would be well-served if you could tell secrets to people you didn't trust and then stop them from passing them on. But you can't. It's a stupid idea. Wanting it badly is not enough.
Nothing like having a hard-copy for peace of mind. But if you attempt to print the page, all you will see is "printing is not allowed by the sender of this message." This is due to abuse of @media print CSS rules to hide the main content when printing. The Style Editor tab of the Firefox Web Console (Menu > Web Developer > Web Console) makes it easy to comment these out. Alternatively, click the eye-shaped icon on the left to disable the CSS style sheet completely.
Archiving self-destructing Gmail messages with Firefox