10th March 2025
tl;dr This was caused by an incompatibility between packages installed and managed by APT and Snap. Running sudo snap refresh resolved the issue.
With non-technical parents, I usually play the role of tech support. Each of them has a second-hand laptop on which I've installed Xubuntu 22.04. I installed Linux in the hope that it reduces the potential for them to get scammed by fake technical support people that may call them and chose Xubuntu over Ubuntu with the idea that the lighter desktop environment would mean extending the life of the laptops. I have some familiarity with Linux, so don't mind troubleshooting issues, but I think if they lived further away it would be less viable due to having to support them over the phone or with something like Teamviewer.
This past weekend we were at their house and they both mentioned that Firefox was nagging them to update, so I took the opportunity to sudo apt update && sudo apt upgrade, shut the computers down again and thought nothing more of it.
Cut to today, when I get a call to say that neither of them can login to their computer. After taking a look they both seem to boot and login correctly, but desktop icons do not appear, window frames do not appear and the mouse cursor was invisible (but somewhat usable if you could figure out where it was). My initial assumption was that it was an issue with one of the updates, so I ran updates again and rebooted in the hope a patch may have come out in the meantime, but that didn't seem to help.
After some Googling and following fruitless trails, I checked the contents of .xsession-errors and discovered error messages relating to Firefox. What I'd forgotten was that in Xubuntu 22.04, Firefox is installed as a Snap package, rather than using APT. This meant that not only had Firefox not been updated when I installed APT updates, there was now some incompatibility in versions that was causing the entire operating system to become unusable. After running sudo snap refresh and rebooting, Firefox got updated and everything was back to normal.
One of the nice things about Linux was being able to run a single command that would install all updates while maintaining compatibility between packages. Now that we have multiple package managers we're vulnerable to issues like this. What's more concerning is the fact that failing to update the Snap packages at the same time as APT should cause such catastrophic failures in the basic functioning of the operating system. Firefox isn't the only package managed by Snap and the list includes a couple of packages relating to Gnome, but it seems strange that those could cause issues when we aren't using Gnome.