Patrick Lamber
Patrick Lamber Microsoft Office Development MVP

Mozilla Firefox throws Error loading debug manifests when debugging and SPFx solution using Modern Pages

It is common practice to debug a SharePoint Framework solution using Modern pages.

I recently developed some SPFx solutions using a slightly different development setup as usual. Instead of using Edge or Chrome for debugging, I used the latest version of Mozilla Firefox.

Once I started my debugging session, I received a well-known error message after hitting the Load debug scripts operation.

Error loading debug manifest

Error loading debug script. Ensure the server is running and the "debugManifestFile" parameter URL is correct.

Usually, you get this error message if you do not serve your solution using the gulp serve –nobrowser command or if you forgot to trust the self-signed certificate using the gulp trust-dev-cert command. In my case, I was sure that both things happened.

After a while, I figured out that Mozilla Firefox was ignoring the trust performed by the gulp trust-dev-cert command. I had to navigate to the served URL https://localhost:4321 directly using the browser.

From there, I manually accepted the risk and continued the navigation. Mozilla Firefox started trusting my self-signed certificate. Afterward, my SPFx solutions worked fine also with Mozilla Firefox.

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