May worth to take a look at this:

1. Allow third party cookies for AWS domains o Go to Settings → Privacy & Security → Cookies and Site Data. o Add exceptions for:  *.awsapps.com  *.signin.aws.amazon.com  .device.sso.
2. Disable Enhanced Tracking Protection for AWS o Visit your AWS SSO login page. o Click the shield icon in the address bar. o Turn off tracking protection for that site.
3. Check extensions and privacy settings o Run Firefox in Troubleshoot Mode (Help → Troubleshoot Mode). o Try logging in — if it works, an extension or privacy setting is interfering.
4. Try a different profile o Create a new Firefox profile (about:profiles). o Log in with that profile to see if the issue persists.
5. Force manual login o If using aws sso login from the CLI, copy the URL manually into Firefox instead of letting the CLI auto open Chrome. o This ensures the correct browser session is used.

https://repost.aws/questions/QU_DPIeGIFR9SF2oxhfDp-nA/issue-aws-sso-login-always-fails-once-before-success-at-least-in-firefox

Hello there,

Warm Greetings !

Thank you for reaching out to us with your concern.

I understand that you encounter an error 'It's not you, it's us' when you try to login via IAM Identity center on Firefox but it works successfully on Google Chrome.

Since the login works successfully on Google Chrome but encounters issue only in Firefox then this confirms that the issue is not related to incorrect configuration made at IAM Identity Center end but rather the problem likely stems from a Firefox configuration or an extension.

To begin with, I would like to set in the right expectation here that such issues which are specific to browsers fall out of scope of AWS PS [1]. I regret any inconvenience this might cause. Having said that, on a best effort basis I would like to share the following points that you may check at your end:

1. Allow third party cookies for the AWS domains mentioned in this documentation [2] o Go to Settings → Privacy & Security → Cookies and Site Data. o Add exceptions for domains mentioned in the linked document
2. Try Private Browsing: Use Firefox’s private browsing mode to see if the issue persists. This mode uses default settings and disables most add-ons.
3. Disable Enhanced Tracking Protection for AWS.
4. Check extensions and privacy settings o Run Firefox in Troubleshoot Mode (Help → Troubleshoot Mode).
5. Try logging in via a different profile
6. Force manual login o If using aws sso login from the CLI, copy the URL manually into Firefox instead of letting the CLI auto open Chrome. o This ensures the correct browser session is used.
7. Check Security Settings: Review your Firefox security settings. High security or privacy settings might block certain web functionalities needed for IAM Identity center.

If the issue still persists, then you may try checking with Firefox support team [3] as they would have the correct expertise and visibility into such issues.

Hoping that the above helps.

References

[1] https://aws.amazon.com/premiumsupport/faqs/#issues-supported

[2] https://docs.aws.amazon.com/singlesignon/latest/userguide/enable-identity-center-portal-access.html

[3] https://support.mozilla.org/en-US/