That error occur in Firefox first of all. You should file the bug
to bugzilla.mozilla.org.
When I visit https://y.st/ I get the following message from IceCat:
An error occurred during a connection to y.st. Peer’s
Certificate has been revoked. Error code:
SEC_ERROR_REVOKED_CERTIFICATE
IceCat offers no option to accept the certificate anyway. All it
presents me is a "Try Again" button. I'm helpless.
I know all certificates should verify, but browser authors and
webmasters are dumb. Honestly, I think the certificate system is doomed
to be broken forever, and everyone will have to use "wget
--no-check-certificate" all the time.
I would switch to another browser to view this site, but:
* Midori crashes all the time
* GNOME Web is slow and takes up too much screen space (bulky,
"modern" widgets)
* Chromium is probably nonfree
* QupZilla is probably nonfree, because it contains Qt5 Web
Engine, which is a component of Chromium, which is probably
nonfree
* Lynx, Links, wget, w3m and eww shouldn't be the only options to
view a webpage
* Links2 and Netsurf are the ugliest things on the planet
* Surf (suckless.org) and Uzbl are too minimalistic, and only a
step up from Links2, and won't even render Riot correctly
* IceWeasel produces the same result
* Abrowser produces the same result
--
http://gnuzilla.gnu.org