In Firefox, go to the admin panel and middle-click on “Users”
Actual behavior:
I get a page saying “The requested page does not exist, or it is private” (roughly translated from German). The URL of that page is https://DOMAIN/admin/users/list.
I can reproduce this on @cpradio’s sandbox, which is running Discourse 1.5.0.beta11. However, it works as expected on our instance, which is still on Discourse 1.5.0.beta6.