Sensing an opportunity in Facebook's squandering of public trust through its previously unrestrained giveaway of user data, Mozilla on Tuesday unveiled a defense against the social ad biz in the form of an add-on for Firefox called Facebook Container.

The Firefox add-on, as its name suggests, attempts to contain Facebook's tracking attempts, in an effort to provide refuge from the internet advertising panopticon.

Along similar lines, Mozilla last week said it would stop advertising on Facebook in an effort to encourage CEO Mark Zuckerberg to improve Facebook privacy settings. It also said it plans to implement a basic ad filter in Firefox later this year.

Mozilla began developing Containers for Firefox in 2016 and started deploying them last year. The technology provides a way to create contexts (tabs) in which browser-based data – cookies, indexedDB, localStorage, and cache – can be sandboxed.

Containers extend the browser's same-origin security model by adding an OriginAttribute called userContextId . So when browsing example.com in a Container named Work, for instance, any resulting cookies would be limited to that container. They would not be accessible if browsing in a different Container.

Facebook Container implements a Container specifically for Facebook, to restrain its informational reach – Facebook tries to track interactions on third-party websites that have implemented Facebook technology such as the Like button or Facebook Login.

"The Add-on keeps Facebook in a separate Container to prevent it from following your activity on other websites," the Facebook Container code repository explains. "When you first install the add-on, it signs you out of Facebook and deletes the cookies that Facebook uses to track you on other websites."

In a blog post, Nick Nguyen, Mozilla's VP of Firefox Product, says, "As a user of the internet, you deserve a voice and should be able to use the internet on your own terms."

It's an ironic choice of words since it's common to browse the internet under someone else's terms – the terms of service asserted by internet sites that disavow user privacy. (Veteran observers of this space may recall Facebook openly abandoned any pretense of privacy in 2011 when it replaced its Privacy Policy with a Data Use Policy.)

Nguyen describes Facebook Container as a tool to protect against the unanticipated consequences of internet usage, albeit a limited one.

"The type of data in the recent Cambridge Analytica incident would not have been prevented by Facebook Container," he said.

"But troves of data are being collected on your behavior on the internet, and so giving users a choice to limit what they share in a way that is under their control is important."

Facebook Container is far from a complete privacy system. Other tools are necessary too. There's Tor and Tails for the hardcore, but any diminished attention from marketers may be balanced by greater attention from authorities suspicious of those who would hide.

Lesser privacy that can be had from a patchwork of browser add-ons – uBlock Origin, Privacy Badger, Disconnect, NoScript, etc. – though these can sometimes break websites. And then there are network privacy issues, some of which may be helped by using a VPN (ideally, that you run yourself).

Even so there are browser fingerprinting techniques that may see through defenses.

While Facebook Container may help a bit, it has limitations. For example, Facebook ads employ links that pass tracking IDs outside the Facebook Container, making it possible for third-party ad firms to associate Facebook authenticated profiles with an external profile.

SO, the only way to win remains not to play. ®