To inspect stacks you need to be in a "privileged" user-mode. Often stacks set the usermode to unprivileged upon startup to prevent accidental / nefarious edits. To change this, and be able to inspect the stack:

1.) Open the stack.

2.) Type Alt-M to open the message box.

3.) Type "set the usermode to 5" and press enter. (This sets the usermode to the highest level).

4.) If the menubar isn't showing, type "show menubar" into the message box and press enter.

Voilla! Full access to edit and inspect the stack. (Note that all changes are lost when you close the tab - the emulator does not yet have persistent storage).