You can check for issues with Total Cookie Protection.

• https://support.mozilla.org/en-US/kb/total-cookie-protection-and-website-breakage-faq
• https://support.mozilla.org/en-US/kb/introducing-total-cookie-protection-standard-mode

This issue can be caused by corrupted cookies or blocked cookies.

• check the permissions for the domain in the currently selected tab in "Tools -> Page Info -> Permissions"

You can try these steps in case of issues with webpages:

You can reload webpage(s) and bypass the cache to refresh possibly outdated or corrupted files.

• hold down the Shift key and left-click the Reload button
• press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• press "Command + Shift + R" (Mac)

Clear the Cache and remove the Cookies for websites that cause problems via the "3-bar" Firefox menu button (Settings).

"Remove the Cookies" for websites that cause problems:

• Settings -> Privacy & Security
  Cookies and Site Data: "Manage Data"

"Clear the Cache":

• Settings -> Privacy & Security
  Cookies and Site Data -> Clear Data -> [X] Cached Web Content -> Clear

• https://support.mozilla.org/en-US/kb/clear-cookies-and-site-data-firefox
• https://support.mozilla.org/en-US/kb/how-clear-firefox-cache

Start Firefox in Troubleshoot Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration or if userChrome.css/userContent.css is causing the problem.

• switch to the Default System theme: "3-bar" menu button or Tools -> Add-ons -> Themes
• do NOT click the "Refresh Firefox" button on the Troubleshoot Mode start window

• https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

• https://support.mozilla.org/en-US/kb/enhanced-tracking-protection-firefox-desktop
• https://support.mozilla.org/en-US/kb/smartblock-enhanced-tracking-protection
• https://support.mozilla.org/en-US/kb/trackers-and-scripts-firefox-blocks-enhanced-track

Thanx a lot for your answers.  :) I haven't time today, hopefully I can see into it tomorrow... /henrik

@Dropa: The Private Mode didn't make any change.

@cor-el: As far as I understand what you wrote, I have tried the troubleshoot possibilities -- without solving the problem.

Sorry, but the problem still is there...  ;o)

Dear Henrik Denmark,

Thank you for reaching out to the Firefox Support Forum with your question. I understand that you are experiencing an issue when trying to sign in to the learning.martinus.dk website using Firefox, and you receive a "406 Security Incident Detected" error.

Based on the error message you provided, it seems that your request is being blocked due to a possible poor reputation of the public IP address assigned to you by your internet service provider. However, you mentioned that your IP address (80.208.65.123) is not suffering from a poor reputation and that you can sign in without any problems using other browsers like Chrome.

To troubleshoot this issue, I would recommend trying the following steps:

Clear your Firefox browser cache and cookies: Sometimes, cached data or cookies can cause conflicts and lead to unexpected errors. You can clear the cache and cookies by going to the Firefox menu (three horizontal lines in the upper-right corner) > Options > Privacy & Security > Cookies and Site Data > Clear Data.

Disable any Firefox extensions or add-ons: Certain extensions or add-ons may interfere with website functionality. Temporarily disable all extensions and add-ons, then try signing in again to see if the issue persists. If the problem is resolved, you can enable the extensions one by one to identify the specific one causing the conflict.

Reset Firefox settings: If the above steps don't resolve the issue, you can try resetting Firefox to its default settings. This will revert all settings to their original state, but it will also remove your bookmarks, saved passwords, and other data. To reset Firefox, go to the Firefox menu > Help > Troubleshooting Information > Refresh Firefox.

If none of the above steps help, it might be beneficial to reach out to the administrators of the learning.martinus.dk website for further assistance. They may be able to provide specific insights into why the security incident is being triggered when using Firefox.

I hope these suggestions help in resolving the issue you are facing. If you have any further questions or need additional assistance, please don't hesitate to ask. We are here to help you.

Best regards, Suram Firefox Support Volunteer

Hi Suram

Thanx a lot for your suggestions.

When I reach "Reset Firefox settings", my danish Firefox only have these relevant (?) items:

- troubleshoot state - more technical info

I'm ready to reset but how?  ;o)

(maybe I'm away from my pc until monday...)