We're experiencing problems with the calendar in Outlook Web App with Hosted Exchange 2013. Chrome had the same problem for a few months until a recent update. Basically we can't see the list of calendars to view and no events are shown in the calendar view, not sure when the error appeared but it was working a couple of months back. See a post at the chromium bug forum for more details on the problem, https://bugs.chromium.org/p/chromium/issues/detail?id=421440. We experience this issue on a clean Firefox with no addons.