This rare error message seems to mean there is a problem with the server’s OCSP response: OCSP «stapling» — inclusion of the verification of the non-revocation of the server’s certificate — is required but not provided.
When I load https://wiki.samba.org/index.php/Main_Page directly I don’t get an error.
Are you using a proxy? There was a reference on another site to an issue using Zscaler on that site: https://access.redhat.com/discussions/2408091 (June 30, 2016).
Does it make any difference if you toggle this setting:
(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.
(2) In the search box above the list, type or paste ocsp and pause while the list is filtered
(3) Double-click the security.ssl.enable_ocsp_must_staple preference to switch the value from true to false
Then try the site again, bypassing the cache (e.g., Ctrl+Shift+r when you reload). Any difference?