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Firefox CORS and REST API preflight failure on custom B2B webhooks

Firefox Web compatibility
jbr replied
Tony Long
Tony Long

Hello Mozilla Support Community,

We are troubleshooting a cross-origin resource sharing (CORS) issue specifically occurring in recent Firefox releases when processing custom B2B appointment requests.

Setup & Context:

Our production application, Frontline Sales Consultancy (flsc.co.uk), triggers a client-side fetch request to an external CRM gateway.

The request works seamlessly on Chrome and Edge, but Firefox throws an NS_ERROR_DOM_BAD_URI during the OPTIONS preflight check.

Observed Behavior:

Firefox Web Developer Console shows the preflight request failing before headers are evaluated.

Access-Control-Allow-Origin and Access-Control-Allow-Methods are explicitly declared on our origin server.

Does Firefox handle strict MIME-type checking or preflight caching differently for custom HTTPS API endpoints?

Any insights into Firefox-specific CORS strictness or network console debugging flags would be greatly appreciated.

Thanks!

Hello Mozilla Support Community, We are troubleshooting a cross-origin resource sharing (CORS) issue specifically occurring in recent Firefox releases when processing custom B2B appointment requests. Setup & Context: Our production application, Frontline Sales Consultancy (flsc.co.uk), triggers a client-side fetch request to an external CRM gateway. The request works seamlessly on Chrome and Edge, but Firefox throws an NS_ERROR_DOM_BAD_URI during the OPTIONS preflight check. Observed Behavior: Firefox Web Developer Console shows the preflight request failing before headers are evaluated. Access-Control-Allow-Origin and Access-Control-Allow-Methods are explicitly declared on our origin server. Does Firefox handle strict MIME-type checking or preflight caching differently for custom HTTPS API endpoints? Any insights into Firefox-specific CORS strictness or network console debugging flags would be greatly appreciated. Thanks!

All Replies (1)

jbr
jbr
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What does mozregression point to?

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