I have to say this is surprising. I hope that one of the developers / maintainers will comment -- just for my edification. I would not have expected a simple bungled application to mess itself up so permanently that it's impossible to get it to run again! That's the sort of thing I'd be less surprised to see in Windows. It happens on that system because some installation processes and applications write cryptic stuff to locations in the registry, and no amount of spelunking will ferret it out. Over the years I've learned what to avoid.
But in Linux it has always been about dependencies and repositories, if I understand correctly. Complete removal of an application should get rid of any hangovers in its settings that might prevent a future installation of said application from running.
After adding the cassandra distribution to my repository list I was able to completely remove and then re-install sunbird. I even did it old-Windows-style -- rebooting after the removal, and then again after the installation. When I click on the sunbird application launcher I get the "busy" cursor for a while and then nothing.
With the exception of the busy cursor, the same thing happens if I try to launch the application from Alt+F2 dialog or from gnome-terminal. Nothing.
Synaptic reports no broken packages. Can't find anything that seems to apply in any of the logs. Launching with admin privs does nothing. It's almost as though the OS and this application are deliberately shining me on!
Absent some pretty quick response from someone I guess I'll go to bare metal and start over again. I won't give up on Linux Mint that easily, and it isn't that hard to reinstall in any case. This time I'll be a good boy and not do the updates, regardless what conventional wisdom outside this forum seems to indicate.
But I have to admit that this has me concerned. Nothing outside my user profile was touched. If I log on to another user account, I am able to run Sunbird. But that really isn't the way things should work, is it?
One more request for suggestions. Many thanks for attempts at aid so far.
I'll leave all of my musings above for anyone who is wondering if I'm an idiot so that there will be no doubt.
Since Sunbird could be launched under another user account I looked at the data locations of both accounts to see if I could see differences. The screwed-up account's default data location for Sunbird had a file called blocklist.xml in it, and that file was not present in the working account's default data location. The non-working data location also did NOT contain a .parentlock file, which the working location did.
Not being married to anything in the non-working data location anyway, I just deleted it. Then Sunbird started right up.
This perplexes me. If someone can propose an explanation I'd appreciate it. A borked data location doesn't seem a good enough reason for an application to outright refuse to start -- at least not to me. I would think the best mode of failure would be for it to come up to a start screen and say, "Hey, dummy, your data is borked!"
Or something along those lines.
Thanks for "listening." And I really would appreciate it if someone can help me understand what happened. I'm new to Linux and am trying to learn.