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Firefox Private Browsing: What It Protects You From (And What It Doesn't)

#firefox #privacy #javascript #browser

Firefox's Private Browsing mode is widely misunderstood. Here is what it actually does, and what it does not do.

What Private Browsing does

When you open a Private Browsing window in Firefox (Ctrl+Shift+P / Cmd+Shift+P):

It prevents:

  • Saving your browsing history locally on this device
  • Saving cookies and site data after the window closes
  • Saving form inputs and search history locally

When you close the Private Browsing window, Firefox deletes all of these from the device.

What Private Browsing does NOT do

Your ISP can still see your traffic: Private Browsing does not hide your activity from your Internet Service Provider. They see which servers you connect to.

Your employer/school network can still see: If you are on a managed network, network administrators can see your traffic regardless of Private Browsing.

Websites still see your IP address: Sites you visit know your IP address. Private Browsing does not mask this.

You can still be tracked within a session: Advertisers can use fingerprinting (device characteristics) to identify you during a Private Browsing session, even without cookies.

What Private Browsing is actually good for

  • Shared devices: Using a family computer or a friend's laptop. Your browsing does not persist after you close the window.
  • Gift shopping: Preventing purchase history from showing up in recommendations on a shared account.
  • Temporary sessions: Quickly checking a site while logged in as yourself somewhere else.

For stronger privacy

Firefox offers options beyond Private Browsing:

Enhanced Tracking Protection (always on): Blocks known trackers in regular browsing mode. Set to "Strict" in about:preferences#privacy for more comprehensive blocking.

Firefox Multi-Account Containers: Isolates your browser sessions so different services cannot track you across sites.

A VPN: Hides your IP address and encrypts traffic from your ISP.

Extensions and Private Browsing

Extensions do not run in Private Browsing windows by default. To allow an extension in Private Browsing:

  1. Go to about:addons
  2. Click on the extension
  3. Toggle "Run in Private Windows" to "Allow"

The extensions in this series (Daily Planner, Habit Tracker, etc.) can be enabled in Private Browsing if needed.

For more on Firefox extensions: full series.

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