Capture Localhost with Fiddler in Firefox

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Fiddler Classic Windows
Martyn
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Martyn asked on 26 Oct 2021, 11:16 PM

According to Telerik docs, localhost should be automatically captured when capturing is enabled in Firefox and FiddlerHook is installed.

Even though this has been working successfully on my desktop for several years, it has stopped working after the latest Firefox update (to v. 93.0 (64-bit) even though FiddlerHook is still present within Firefox. Note that all non-localhost traffic is still captured as expected. Localhost will be captured if the FiddlerFox extension is installed and enabled, but this requires manually toggling a switch control in FiddlerFox while using Fiddler.

Is this functionality now broken, and, if so, can it be fixed?

 

Thank you very much,

Martyn

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Nick Iliev
Telerik team
answered on 27 Oct 2021, 07:55 AM

Hi Martyn,

 

Mozzila recently changed the default behavior for proxying localhost addresses (localhost, 127.0.0.1:8 and :1), so you will need to change these default settings if you wish to be able to capture traffic directed through localhost. In Mozzila, open about:config and modify the key network.proxy.allow_hijacking_localhost below to true. You should be able to start capturing localhost traffic immediately.

 

Regards,
Nick Iliev
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Martyn
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commented on 28 Oct 2021, 09:32 PM

Good Morning Nick,

Thank you for responding so quickly and for providing your invaluable, and correct, response. I messed around with this issue for a while and performed related online searches, but couldn’t find a solution.

Regards,

Martyn

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Fiddler Classic Windows
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Martyn
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Nick Iliev
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