In Firefox desktop, we have two prefs used to enable/disable the feature "First Party Isolation" (also called "double keying"), which prevents third parties from tracking users across multiple websites. - privacy.firstparty.isolate [1] - privacy.firstparty.isolate.restrict_opener_access [2] Now we are going to add these two prefs into mobile.js so that Fennec users can also opt in to use this privacy feature. They'll be disabled by default and there will be no menu settings for them. So it would be a kind of hidden feature. However, we plan to design a specific mode (such as Tor Mode or Onion Browsing), which will enable FPI as well as fingerprinting resistance and other Tor features at once. [1] Added in bug 1260931. Used to enable First Party Isolation. [2] Added in bug 1319773. Controls the access of window.opener for different first party domain. See the detail in https://bugzilla.mozilla.org/show_bug.cgi?id=1319773#c22.

Comment on attachment 8869348 [details] Bug 1358361 - Move prefs of First Party Isolation and resist fingerprinting to all.js. https://reviewboard.mozilla.org/r/140984/#review144566

Pushed by jhao@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/e52428cb04a0 Move prefs of First Party Isolation and resist fingerprinting to all.js. r=Gijs