Outlook Beta broken

Got this same 'Owa.mail is undefined' error yesterday.  Had been on the Outlook Beta a couple of weeks without issue via Firefox.  Refreshing the page triggered the error (often required because both new and old versions can go hours without checking for mail!)  None of the suggestions mentioned here cleared it.  However, a simple full refresh worked (in Firefox, clicking Refresh while holding down [Shift]).  But the error returned when I performed another normal Refresh, so have turned off the Beta.  Everything is working again now.

It is poor form for Microsoft not to offer an option to turn off the Beta or go into a safe mode from the error screen, not to provide info on this bug, not to fix it after many months, and not to provide priority error logging to Beta users.