Configure Fiddler for Web App proxy:

To get Firefox running with Fiddler, you need to:

  • Configure Firefox to proxy its traffic to Fiddler.
  • Configure Firefox to trust Fiddler’s root certificate.

Configuring the Proxy

  1. Firefox’s proxy settings are found by opening its Tools menu, clicking the Options item, and opening the Advanced settings. Select the Network tab. At the top of the tab, click the Settings… button to the right of Configure how Firefox connects to the Internet.

2. You may manually configure Firefox to send traffic to Fiddler by entering the IP address and port (by default, and 8888) in the appropriate boxes:

Trusting the Certificate


  • If Fiddler is configured to decrypt HTTPS traffic (Tools > Fiddler Options > HTTPS), you will find that attempting to load a HTTPS page in Firefox yields a scary warning message.
  • This message is shown because Firefox does not use the Windows Trusted Certificate Authority list; it instead has its own list of trusted certificates.
  • First, we need a copy of Fiddler’s Root certificate. Inside Fiddler, click Tools > Fiddler Options. On the HTTPS tab, Select Actions and click the Export Root certificate to Desktop button at the bottom. This will create a file named FiddlerRoot.cer on your desktop.

  • Next, we must import this certificate into Firefox’s Certificate Manager. Firefox’s certificate settings are found by opening Firefox’s preferences → Privacy and Security and scroll down to certificates section and select “View Certificate”

  • In the Certificate Manager, click the Authorities tab, and the click the Import button at the bottom:

  • In the Select File containing CA certificate(s) to import box, choose the FiddlerRoot.cer file that you saved to your desktop a moment ago, then click Open.
  • In the screen that appears, check the Trust this CA to identify websites box at the top, then click OK.
  • With this change in place, Firefox will now trust the Fiddler root certificate. Visiting HTTPS pages in Firefox with Fiddler capturing will no longer show certificate error pages.

  • You can inspect and tamper any request by clicking on the specific request and selecting Inspect option.
  • If you want to resend/edit the request and submit, use Composer option in fiddler to edit the request and submit



Categories: Proxy Tools


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