Our internal server sends the Strict-Transport-Security header but it does not work on Firefox for Android. It works on the PC but not on the mobile phone. Max-Age is set to 31536000 seconds (1 year). Now when I access our servers via https, the browser saves the HSTS policy. Now I close Firefox on the PC and then I open Firefox and press F12 to see the connections. If I now access http://example-internal-server.local the browser overwrites the request with HTTPS as expected.

But on Firefox for Android it doesn't work as expected. On my mobile I open https://example-internal-server.local again so that the browser can save the HSTS policy. Now I close Firefox and reopen Firefox. Now I visit http://example-internal-server.local and expect Firefox to automatically convert the unsafe request to HTTPS because of HSTS. Which he's not. What's going on here?