Blog | G5 Cyber Security

Burp Suite Not Intercepting Firefox Traffic

G5 Cyber Security

TL;DR

Burp Suite isn’t intercepting your Firefox traffic? This guide covers the most common fixes, from browser settings to certificate issues and proxy configurations.

Fix Burp Suite Not Intercepting Firefox Traffic

  1. Check Burp Suite is Running and Listening
    • Make sure Burp Suite Professional (or Community) is actually running.
    • Verify the Proxy listener is active. Go to Proxy > Options in Burp Suite. The ‘Listener’ tab should show a listening address (usually 127.0.0.1:8080).
  2. Configure Firefox to Use Burp as its Proxy
    • Open Firefox settings.
      Type about:preferences#general in the address bar and press Enter.
    • Search for ‘Network Settings’. Click on ‘Settings…’.
    • Select ‘Manual proxy configuration’.
    • Set HTTP Proxy to 127.0.0.1 and Port to 8080 (or the port Burp Suite is listening on).
    • Ensure ‘Use this proxy server for all protocols’ is checked.
    • Click OK.
  3. Install the Burp CA Certificate in Firefox

    This is often the root cause of interception problems.

    • In Burp Suite, go to Proxy > Options and then the ‘Certificate’ tab.
    • Click on ‘Export’. Save the certificate (usually as a .der file). Choose a location you can easily find.
    • In Firefox, type about:preferences#privacy in the address bar and press Enter.
    • Scroll down to ‘Certificates’ and click ‘View Certificates…’.
    • Select the ‘Authorities’ tab.
    • Click ‘Import…’.
    • Browse to the .der file you saved earlier and open it.
    • A dialog will appear asking how much you trust the certificate. Check all boxes (Trust this CA to identify websites, Trust this CA to identify email users, Trust this CA to identify software developers) and click OK.
  4. Restart Firefox

    A full restart is crucial for the changes to take effect.

  5. Check Burp Suite Interception Rules
    • Go to Proxy > Options in Burp Suite.
    • The ‘Intercept’ tab allows you to define rules that control which traffic is intercepted.
    • Ensure the rules aren’t blocking the traffic you expect to see. Start with ‘Intercept all requests and responses’.
  6. Clear Firefox Proxy Settings (and try again)

    Sometimes, old proxy settings can interfere.

    • Return to about:preferences#general in Firefox.
    • Set Network Settings back to ‘Use system proxy settings’ or ‘No proxy’.
    • Restart Firefox.
    • Then repeat step 2 to reconfigure the proxy with Burp Suite’s details.
  7. Check for Conflicting Extensions

    Some Firefox extensions can interfere with proxy settings or SSL/TLS connections.

    • Disable any security, privacy, or network-related extensions temporarily to see if they are the cause. You can manage extensions via about:addons
  8. Verify Burp Suite’s SSL/TLS Configuration

    If you’re intercepting HTTPS traffic, ensure Burp Suite is configured correctly.

    • Go to Proxy > Options in Burp Suite.
    • The ‘SSL’ tab should have the Burp CA certificate installed and enabled.
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