in the latest version of the Java launcher for windows, when you click on the link for the snapshot it tries to connect you to:

https://.minecraft.net/article/minecraft-snapshot-18w43a?ref=launcher

which isn't recognized as a page because the url (after the https part) starts with a period.

If you get rid of that first period it works fine though.  The problem isn't with the webpage it's supposed to go to, just with the launcher trying to open a page that doesn't exist.