Whenever I try to add an instance account, Thunder appears to replace the instance I'm already logged into with the new one, so I can only browse one instance at a time. Is this behaviour intended? If so, will support for multiple instances be added later?
If you go to the far right lower tab you will see your user listed at the top. Click on that and you will see a list of accounts you have added. You can switch accounts here and then go back to the lower left tab to see the instance at the top with similar behaviour.
That is my understanding as a user, it seems sane if a little clunky.
This is what I've been doing to log into new instances, but it always seems to just replace the instance I was already logged into with the new one. The UI looks like it's supposed to show a list of instances and the button says "Add account", but the list is always empty, no matter if I've logged into other instances before.
That seems odd. Are you perhaps removing your account before adding another? This would happen if you are using the log out option to access the account list, instead of the account button.