Sunbird does not show Events any more

As of today, a Sunbird 1.0b1 installation on a computer stopped showing the calendar contents. The top right just shows a rotating loading indicator and nothing happens, all the directly calendar-related menus are disabled.

The error console shows the following messages:

rootComp is null
file:///C:/Program%20Files%20(x86)/Mozilla%20Sunbird/modules/calUtils.jsm -> file:///C:/Program%20Files%20(x86)/Mozilla%20Sunbird/calendar-js/calIcsParser.js    line 82

Error selecting events with recurrence!
[Exception..."Unexpected error" nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)" location "JS frame :: file:///C:/Program%20Files%20(x86)/Mozilla%20Sunbird/modules/calUtils.jsm -> file:///C:/Program%20Files%20(x86)/Mozilla%20Sunbird/calendar-js/calStorageCalendar.js :: cSC_getEventFromRow :: line 1192" ata: no]
DB Error: not an error    line 237

The only change to the system that I can think of is that I tried updating Mozilla Firefox 29 to the current version (by opening the about box, waiting till the "downloading update" message was replaced with the notice to restart Firefox, though after restarting, it still seemed to be version 29) - does one Mozilla software such as Firefox mess around with files of another, such as Sunbird?

In any case, How can I fix Sunbird or at least find and retrieve the data in a useful format?

Concerning Sunbird: I am aware that Sunbird is not being actively developed any more, and when the decision was made to stop development on Sunbird in 2009, I had suggested to the owner of said computer to switch to another calendar software because updates were going to cease. Unfortunately, the user refused to do so, stating that the latest version of Sunbird published has everything they need (hence future updates were deemed unnecessary, if not harmful), and moreover, the most straightforward alternative, Lightning, was/is only available as a Thunderbird plugin, and the user in question definitely did not want to migrate away from Windows Live Mail.

P.S.: Unfortunately, there is no Sunbird tag, and my reputation is not sufficient to create one. The Lightning project should be the closest thing, so I have still added that tag.

The cause of the problem was that accidentally, a file that Sunbird cannot open was passed as a command line argument (as an adjacent icon had accidentally been dragged and dropped onto the Sunbird shortcut icon in a hasty move).

Presuming that whatever the user tries to open with Sunbird must be a calendar, that prompted Sunbird to add the passed file as an additional calendar and, failing to open the file format (it was an MS-DOS Batch file), the JavaScript responsible for parsing the file choked and the whole calendar data failed to load.

The problem was not immediately apparent as the user had minimized the calendar list (i.e. moved the split separator between the list of calendars and the calendar table to the window edge, so the list of calendars was invisible), hence the presence of a new "unnamed calendar" was not obvious.