# Install Burp's CA Certificate In Firefox

1. In Burp Suite, go to **Proxy** > **Intercept** tab and disable intercept mode by clicking on the "**Intercept is on**" button. 

![](https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-Lfu0O3v4hh3tZFmLPDz%2F-Lfu0SttiyNdVe2wQV5_%2Fimage.png?alt=media\&token=78366c8f-2f88-47f4-ba68-3d4fbeb1d42d)

<div align="left"><img src="https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-Lfu0O3v4hh3tZFmLPDz%2F-Lfu0XnPy4IJ8b7CR4jy%2Fimage.png?alt=media&#x26;token=cc68ab52-e10c-4324-a43b-6db3ccdb25db" alt=""></div>

In Firefox, navigate to a secure website, e.g., `https://www.example.com`.

If you have configured Burp's proxy listener correctly, and you haven't installed Burp's self-signed Certificate Authority (CA) certificate, yet, then the browser may throw an "invalid security certificate" error with the message "*...issuer certificate is unknown*". Click on the "Advanced" button to see error details.

![Invalid security certificate](https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LWHQt-EMiiOHTuosAKW%2F-LWHQwRWKP7lajI7tYU3%2F33-cert.png?generation=1547571285726138\&alt=media)

If you received "SEC\_ERROR\_UNKNOWN\_ISSUER" error from the browser, navigate to `http://burp`.

![Download Burp's self-signed root certificate](https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LWHQt-EMiiOHTuosAKW%2F-LWHQwRYK8MDj44MBPMs%2F34-cert.png?generation=1547571286671322\&alt=media)

Click on "CA Certificate" link to download the "cacert.der" file.

![](https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LydRizJwNOZ8NHyXEAi%2F-LydRrwOG0kz9zDOOAGB%2Fimage.png?alt=media\&token=604e4d73-4700-421c-bd81-6e51b5fea0ac)

In the Firefox browser, go to "Preferences", search for the term "certificate", and click on "View Certificates" button.

![](https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LydRizJwNOZ8NHyXEAi%2F-LydRxTeRedRx3TouqbD%2Fimage.png?alt=media\&token=a3215a53-7898-4114-b414-79b076f7ed4d)

In the "Certificate Manager" window, click on "Import" button and select the downloaded "cacert.der" file.

<div align="left"><img src="https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LydRizJwNOZ8NHyXEAi%2F-LydS0MFOY2MmqkYTtLi%2Fimage.png?alt=media&#x26;token=c17c01f8-e236-4dd6-96b5-150863462da3" alt=""></div>

In the "Downloading Certificate" window prompt, select checkboxes as shown in following image and click on "Ok".

<div align="left"><img src="https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LydRizJwNOZ8NHyXEAi%2F-LydS4Zckq3b-phWxkzP%2Fimage.png?alt=media&#x26;token=8f1bc492-4e81-4636-8779-b37f66850ea5" alt=""></div>

Access secure websites, e.g., "<https://www.example.com>", without encountering the "SEC\_ERROR\_UNKNOWN\_ISSUER" error.

![](https://990422818-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LWGXF4oLcghA1GLq0CM%2F-LydRizJwNOZ8NHyXEAi%2F-LydS900uHRkz-DxZwl4%2Fimage.png?alt=media\&token=2cab18d8-96ef-4624-b5d4-3d951dcee87b)


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