<snip>this is a service provider level issue. We will try to sort this out sooner instead of later.
That is great, thank you.
<snip>Microsoft Edge browser
Just wanted to say, this is not a browser vendor or browser version-specific issue. Every modern major and proper web browser will consistently complain about this issue (as long as said browser is set to check & report on this detail, which is the standard default behaviour).
Potentially bad analogy warning
Imagine at a traffic stop, a driver presenting a valid driver's license but just for another driver! Providing another driver's license as own is a red alert for the traffic cop regardless of cop's jurisdiction and age. Likewise for our browsers, any make/version of browser should complain and normally will complain. Unless, for argument's sake, one finds a buggy browser or a browser from decades ago etc.
My desktop version of Firefox doesn't complain, but Chrome on Android does.
For this interesting no-issue case, there must be a reason which applies to that particular browser (or computer); the most usual suspects I have seen are cache-related and browser configuration-directive-related.
To address cache possibility, I suggest this:
1) Try force-refreshing the page with CTRL+F5 which may or may not work (I do not know if it covers certs but it requires only a moment to test).
2) If nothing changes, then completely remove this one particular website unrealworld.fi from web browser's cache (WARNING: stored site passwords removed too!) using this procedure or similar:
https://superuser.com/a/733154To address configuration-directive possibility, I suggest this: Probably easiest way is creating a new Firefox user profile just to test for a moment. A new user profile should not come with any exceptions thus you should see, what we see.