I can reproduce the problem.
Though, in Firefox I still see the URL that should be loaded, but it's locked, just as you describe.
What i see is a list of JS errors in the Console.
We must try basic debugging steps here:
Does the issue also persist with a WordPress Default Theme and NO Plugins BUT the Toolset Plugins?
If not, could you then re-enable the Plugins one after the other, and check the issue each time you enable a plugin?
Please report me when the issue comes back
It might also be due to the Theme.
Please do reactivate your Theme only after you are sure the issue isn't coming form a 3rd Party Plugin.
==> Please also try to avoid any Custom JavaScript in Views or Content templates for the test.
What tells you WP Debug?
Could you enable it shortly and then repeat the steps to see if some error is thrown?
https://codex.wordpress.org/WP_DEBUG
If above steps don't solve things and no errors are thrown I'll need a sites snapshot if possible.
We usually recommend the free Plugin "Duplicator" for this porpoise.
If you already know how Duplicator works
(http://wordpress.org/plugins/duplicator/),
please skip the following steps and just send me the installer file and the zipped package you downloaded.
★ Duplicator Instructions
hidden link
Send me both files (you probably want to use DropBox, Google Drive, or similar services, as the snapshot file will be quite big)
❌ IMPORTANT ❌
Remember to create or keep an admin account for me before creating the snapshot, or I won't be able to login. You may delete the new admin account once the snapshot has been built.
I will enable your next answer as private so you can provide me the information securely.
Please don't hesitate to inform me in case the issue persists
Thank you for your patience.