The new Firefox private browsing mode allows for both non/private browsing windows at the same time. So if a website pops up a new window (which will be in non private mode) can it read stored data?

I know we can block pop-ups, but some websites seem to be able to bypass that. Wasn't it better the old way where private browsing mode was sticky and did not allow any regular mode windows?

2 Answers 2


You're starting with a wrong premise. Pop-ups originating from a Private-Browsing window (legitimate and illegitimate ones) are already started in private-browsing windows.

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can it read stored data?

Yikes, you have the wrong idea about private browsing.

Private browsing/incognito mode/"porn mode" does not affect the browser's ability to read stored data in any way, shape, or form.

It affects the browser's ability to store data. Or, to put it another way, it affects your wife's ability to read your browser history :)

A private browser window can still read your cookies and any other data that are available to a non-private browser window. That being said, a non-private window can't really read much to begin with.

  • 5
    I like the first part of the answer, but the last section is not 100% accurate - private browser is like a sandbox, nothing goes in and nothing comes out. Try this: log into e.g. facebook with "Remember Me". Don't log out, just switch to Private Browsing - you are no longer logged in. See also my answer here: security.stackexchange.com/a/875/33
    – AviD
    Dec 18, 2013 at 8:32

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