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CORS error in Firefox incognito mode only

Amit Kumar Singh
Amit Kumar Singh
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Hi there, I am working on a site with Segment API and need to load their JS on my site for it to work. Whats happening is, I get the following error: "Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://api.segment.io/v1/p. (Reason: CORS request did not succeed). Status code: (null)."

The weird part is, it happens only in Firefox incognito mode. It works on Chrome, Edge, Opera.

I am wondering if this is by design or if it is a bug.

Firefox version 98.0 (64-bit).

Hi there, I am working on a site with Segment API and need to load their JS on my site for it to work. Whats happening is, I get the following error: "Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://api.segment.io/v1/p. (Reason: CORS request did not succeed). Status code: (null)." The weird part is, it happens only in Firefox incognito mode. It works on Chrome, Edge, Opera. I am wondering if this is by design or if it is a bug. Firefox version 98.0 (64-bit).

Valgt løsning

Is it a background request (fetch or XMLHttpRequest), or a regular script tag?

CORS background requests definitely require an Origin header. I wonder whether that is suppressed in private windows with some requests? You could inspect the headers in the Network panel of the Dev Tools. More info on that panel: https://developer.mozilla.org/docs/Tools/Network_Monitor

If it's a regular script tag, this could be due to Tracking Protection (by default, stricter in private windows) or an add-on that blocks analytics scripts. For Tracking Protection, click the shield icon at the left end of the address bar to check what is being blocked. With add-on blockers, the UI varies, but the toolbar button usually gives you an info panel.

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jscher2000 - Support Volunteer
jscher2000 - Support Volunteer
  • Top 10 Contributor
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Valgt løsning

Is it a background request (fetch or XMLHttpRequest), or a regular script tag?

CORS background requests definitely require an Origin header. I wonder whether that is suppressed in private windows with some requests? You could inspect the headers in the Network panel of the Dev Tools. More info on that panel: https://developer.mozilla.org/docs/Tools/Network_Monitor

If it's a regular script tag, this could be due to Tracking Protection (by default, stricter in private windows) or an add-on that blocks analytics scripts. For Tracking Protection, click the shield icon at the left end of the address bar to check what is being blocked. With add-on blockers, the UI varies, but the toolbar button usually gives you an info panel.

Amit Kumar Singh
Amit Kumar Singh Spørgsmålsstiller
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Hi @jscher2000, thanks for the response.

Disabling the Enhanced Tracking Protection worked.