(Reported by mfisherlevine, who regularly uses Firefly in a "traditional" Jupyter notebook run on a development server.)
When afw.display's getDisplay() is run, with a 'firefly' backend, in a non-Nublado notebook environment, the cell produces a line of HTML-formatted output that contains a clickable link to the appropriate display, so that it's easy to open in a new browser.
(NB: in this mode the JupyterLab extension / tab is by definition not available)
When the cell is re-executed with the same kernel, the line of formatted output disappears and is not re-displayed. This makes it difficult to find the correct URL to use.