Latest Fiddler Classic no longer decrypting HTTPS in latest Firefox version

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Fiddler Classic
DLipman
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DLipman asked on 01 Jun 2022, 06:53 PM

With Firefox v101 I can no longer decrypt HTTPS with Fiddler Classic.

I reset Fiddler's Root Certificate multiple times to no avail. 

When the same is tested in MS Edge, no problem

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Nick Iliev
Telerik team
answered on 03 Jun 2022, 06:37 AM

Hello David,

 

We made comprehensive testing with the latest version of 64-bit Firefox on Windows 10 and Windows 11, and the HTTPS traffic capturing is working as expected on our side. That said, you may have a specific misconfiguration that prevents Firefox from using the FIddler proxy properly. 

The first thing to check is if Firefox going through the Fiddler proxy at all? You can check that by trying to capture traffic from non-secure sites like http://example.com

The next thing to try (given that Firefox is configured to use the Fiddler proxy) is to switch the default certificate generator and try using BouncyCastle eventually (learn about the differences and how to change the certificate generator in the following article: https://www.telerik.com/blogs/understanding-fiddler-certificate-generators )

 

 

Regards,
Nick Iliev
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DLipman
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answered on 03 Jun 2022, 12:26 PM

Thank you Nikolay !

The problem seems to have been transitory (FFv101 on Win 7 Ultimate/32).  I tried again this AM with no problems. 
Why I had an issue is unknown. 


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Nick Iliev
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