I REPRODUCED THE BUG IN A VM!!! Looks like it is indeed a timing issue, just like @guiverc said.
OK, so the behavior here is very, very weird - on one test, Firefox was just gone, just like the original post described. Attempting to run it in the terminal resulted in a notice that Firefox wasn’t installed. The next test, Firefox appeared, but I didn’t have the presence of mind to try and launch it… The third test, Firefox appeared, but this time I actually tried and launch it… and it didn’t launch. Trying to run it in a terminal gave me the following error:
error: error running snapctl: cannot invoke snapctl operation commands (here "is-connected") from outside of a snap
ERROR: not connected to the gnome-3-38-2004 content interface.
I thought to look at /var/log/syslog on this third test, and sure enough, Snap failed to start at some point in the boot process.
So, here’s how I made this mess happen:
My physical hardware:
HP Z220 SFF Workstation
Intel Xeon processor E3-1225v2
16 GB of A-TECH RAM (DDR3, 1600MHz, no ECC)
Lubuntu 22.04 ISO is located on a 12TB WD Easystore USB drive. ISO checks as good using sha256sum.
Host OS is Ubuntu Studio 21.10.
Steps:
1: Open a terminal, and cd your way to the ISO location.
2: Fire up a VM with this command:
qemu-system-x86_64 -cpu kvm64 -m 4G ./lubuntu-22.04-desktop-amd64.iso
3. Wait for the OS to load. It will take quite a while, since KVM acceleration is purposefully left off here.
4. Once you get to the desktop, click inside the VM window, navigate to the Application Menu, and hover over “Internet”. Firefox may or may not appear.
5. Hit Ctrl+Alt+T to get a terminal, and type firefox. You may be told that Firefox is not installed, or it might give you an error. Other possibilities may also occur.
6. Run “nano /var/log/syslog”. Search for “failed to start snap”. You may find the Snap error message. (I originally said to use PCManFM-QT here, but since this VM is running using pure emulation, it’s sloooooow, and using nano is quicker.)
I’ve left the QEMU instance from the third test open and paused, so if you want to peek into the guts of a VM with a wonky Snap system and an unlaunchable Firefox, now’s your chance. I did leave the VM running for quite a while after getting it to glitch, so hopefully I’ve not already messed it up. Unfortunately, my Internet is metered, and I gave the VM 4 GB of RAM, so I probably can’t upload a RAM dump, but I can try to replicate the issue again with a 1 GB RAM VM, and if things go haywire, I can probably dump the RAM and upload it.