Note: In this problem, Safe Mode brings no Joy. === First print attempt File > Print Preview provokes this notice: "Print Preview Error" "An error occurred while printing" Behind the error notice is this dialog: "Print Preview" "Title: Troubleshoot Firefox issues using Safe Mode | Firefox Help" "Progress: Preparing..." [_Cancel_] "Preparing..." never goes away. === Thereafter File > Print Preview doesn't work at all (no response). File > Print provokes the error notice above. This problem has often occurred. For some reason I can't rationalize, I think Firefox is attempting to print at the same time that it's preparing the print preview (or maybe I just think that because the notice says "...while printing". Printing (and Print Preview) in the Palemoon browser works every time. FF version 84.0 (64-bit) running in Linux Mint 18.3 running as a VBox Guest with a Win10 Host. The print target directory is in a virtual USB drive plugged into the VM (in both the FF and the Palemoon cases).