Hello, I apologize for this being my first message and for not being in the right place or way.
While searching for a possible problem (which in the end had nothing to do with Firefox) I discovered that there are still problems accessing the Spanish government’s websites.
All government websites use FNMT certificates, which changed around mid-2024. And if the problem persists, it is because the database incorporated by the browser has not been updated.
I tried to report the error to the website’s maintenance team (around sept 2024), but you know how it is with bureaucracy. They kept asking me for additional information from a private domain I couldn’t access (they probably activated an internal communication system that didn’t allow for external participation).
All access problems are resolved by installing the certificates available on this page:
This operation must be done with another browser, since Firefox (correctly) prevents any access to a secure page without a valid root certificate.
Despite all this, the maintenance of secure access tools with Firefox is being carried out correctly, and it remains a perfectly valid means to perform any online administrative operation (with Debian/linux).
But it’s likely that this is limited to long-time users, since it’s unlikely that any new user (especially without advanced knowledge) will be able to correctly install the necessary root certificates.