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Enable dynamic First-Party Isolation (dFPI)

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Works with any Linux distroWorks with any Linux distribution that can run bash scripts.
  • Linux onlyThis script improves your privacy on Linux
  • Single actionThis page belongs to a script, containing basic changes to achieve a task.
  • Impact: Minimum

    System Functionality / Data Loss Risk: Low

    This action improves privacy with minimal impact when you run the recommended script.

  • Bash (Shell script)These changes use Linux system commands to update your settings.
  • Sudo/root requiredThis script requires privilege access to do the system changes
  • Fully reversible

    You can fully restore this action (revert back to the original behavior) using this website.

    The restore/revert methods provided here can help you fix issues.

Overview​

Dynamic First-Party Isolation, also known as dFPI, is an advanced privacy feature in Firefox. This feature commonly referred to as:

  • Total Cookie Protection 1,
  • dFPI (dynamic First-Party Isolation) 2,
  • Dynamic storage partitioning 3.

Essentially, dFPI is an enhanced version of a previous privacy tool known as First-Party Isolation (FPI) 4.

The primary purpose of dFPI is to improve user privacy online. It accomplishes this by preventing third-party websites from accessing or tracking a user's data across different websites 1 3.

By default, this feature is activated for all Firefox desktop users 5.

Within Firefox's settings, there's an option called network.cookie.cookieBehavior which governs how dFPI operates. This setting has three potential values 3:

  • 5: The browser will block known trackers and partition storage for third-party content.
  • 4: Only known trackers will be blocked without any partitioning of third-party storage.
  • 0: All trackers and third-party content are allowed.

This script sets the value to 5, ensuring the highest level of privacy by blocking trackers and partitioning third-party storage. This aligns with recommended privacy practices because even if you choose the 4 value, the older First-Party Isolation (FPI) will still be active 6.

Safe for General Use
All actions in this script is recommended for all users. This is recommended for all users to improve without any noticeable impact on the system functionality.
Sources
PrivacyLearn.com maintains strict sourcing standards for accuracy, integrity and up-to-date content. Our content relies on authoritative sources including vendor documentation, industry standards, and verified research. Learn more about our verification process and quality standards in our editorial standards page.

Apply Now​

Choose one of three ways to apply:

Download script​

Download and run the script directly
  • No app needed
  • Offline usage
  • Free
  • Open-source
Help

How to apply or restore "Enable dynamic First-Party Isolation (dFPI)" using script​

  • ≈ 3 min to complete
  • Tools: Web Browser
  • Difficulty: Medium
  • ≈ 5 instructions
  1. 1

    Download

    Download the script file by clicking on the   Apply protection  button above.
    Use   Undo protection button above to restore changes.
  2. 2

    Keep the file

    If warned by your browser, keep the file.
  3. 3

    Open

    Open the downloaded file.
  4. 4

    Exit

    Once it's done, press any key to exit the window.
  5. 5

    Restart

    Restart your computer for all changes to take effect.

Apply with privacy.sexy​

Guided, automated application with safety checks
  • Recommended for most users
  • Includes safety checks
  • Free
  • Open-source
  • Popular
  • Offline/Online usage
Open privacy.sexy
Help

How to apply or restore "Enable dynamic First-Party Isolation (dFPI)" using privacy.sexy​

  • ≈ 3 min to complete
  • Tools: privacy.sexy
  • Difficulty: Simple
  • ≈ 4 instructions
privacy.sexy is free and open-source application that lets securely apply this action easily with more advanced options.
  1. 1

    Open or download

    Open or download the desktop application
  2. 2

    Choose script

    1. Search for the script name: Enable dynamic First-Party Isolation (dFPI)
    2. Check the script by clicking on the checkbox.
  3. 3

    Run

    Click on ▶️ Run button at the bottom of the page.

    This button only appears on desktop version (recommended). On browser, use 💾 Save button.

Run commands​

Copy and run commands manually Requires technical knowledge
Apply changes
pref_name='network.cookie.cookieBehavior'
pref_value='5'
echo "Setting preference \"$pref_name\" to \"$pref_value\"."
declare -a profile_paths=(
  ~/.mozilla/firefox/*/
  ~/.var/app/org.mozilla.firefox/.mozilla/firefox/*/
  ~/snap/firefox/common/.mozilla/firefox/*/
)
declare -i total_profiles_found=0
for profile_dir in "${profile_paths[@]}"; do
  if [ ! -d "$profile_dir" ]; then
    continue
  fi
  if [[ ! "$(basename "$profile_dir")" =~ ^[a-z0-9]{8}\..+ ]]; then
    continue # Not a profile folder
  fi
  ((total_profiles_found++))
  user_js_file="${profile_dir}user.js"
  echo "$user_js_file:"
  if [ ! -f "$user_js_file" ]; then
    touch "$user_js_file"
    echo $'\t''Created new user.js file'
  fi
  pref_start="user_pref(\"$pref_name\","
  pref_line="user_pref(\"$pref_name\", $pref_value);"
  if ! grep --quiet "^$pref_start" "${user_js_file}"; then
    echo -n $'\n'"$pref_line" >> "$user_js_file"
    echo $'\t'"Successfully added a new preference in $user_js_file."
  elif grep --quiet "^$pref_line$" "$user_js_file"; then
    echo $'\t'"Skipping, preference is already set as expected in $user_js_file."
  else
    sed --in-place "/^$pref_start/c\\$pref_line" "$user_js_file"
    echo $'\t'"Successfully replaced the existing incorrect preference in $user_js_file."
  fi
done
if [ "$total_profiles_found" -eq 0 ]; then
  echo 'No profile folders are found, no changes are made.'
else
  echo "Successfully verified preferences in $total_profiles_found profiles."
fi
Help

How to apply or restore "Enable dynamic First-Party Isolation (dFPI)" using commands​

  • ≈ 2 min to complete
  • Tools: Terminal
  • Difficulty: Medium
  • ≈ 3 instructions
  1. 1

    Open terminal

    Open your terminal application.
  2. 2

    Copy code

    Copy the code:
    Copy Apply Code Copy Revert Code
  3. 3

    Paste & run

    Paste the commands into terminal application and press Enter to run.

    Some changes require a system restart to take effect

Similar Guides​

Wider Goal​

Guides below includes this guide to achieve a wider goal.

See other more general settings that includes this one as one of its actions.

These plans combine multiple privacy settings, including this one, for stronger protection.

Web browsers, including Firefox, save various data types such as cookies, cache, and site-specific details. While this data helps in providing a faster and persona...
Visit category page

Same Goal​

Other guides in Enable Firefox state partitioning (Total Cookie Protection) 

See settings that are in the same category as this guide.

Using other actions in the same category may help you achieve your goal better.

Enable Firefox network partitioning
Disable outdated Firefox First-Party Isolation (FPI)

About the Creators​

These people have authored this documentation and written its scripts:

  • Avatar of undergroundwires. The creator of PrivacyLearn and privacy.sexy. Black and white portrait showing a person wearing a polka dot tie and suit jacket, reflecting the professional expertise behind the privacy protection tools.
    • Certified security professional
    • 7+ years experience securing banks
    • Open-source developer since 2005
    • EU advisor, Public Speaker, Moderator
    • Hundreds across the globe
    • Testers, reviewers, developers
    • Companies, military agencies
    • Community since 2017
About Us

Reviewed By​

This guide has undergone comprehensive auditing and peer review:

  • Expert review by undergroundwires​

    • Verified technical accuracy and editorial standards
    • Assessed system impact and user privacy risks

  • Public review by large community​

    • Privacy enthusiasts and professionals peer-reviewed
    • Millions of end-users tested across different environments

History​

We continually monitor our guides, their impact and all other privacy options. We update our guides when new information becomes available. On every update, we publicly store who made the change, what has been changed, why the change was made and when the change was made.

Review Change History Our Change Process