Inderstandably, VB Guest Additions was removed from the Trisquel repos, as
Trisquel cannot recommend unfree software, even if it's for inside a VM.
I installed the guest additions manually. I guess this is no worse,
ethically, than installing Windows (or any other unfree software) in a
virtual machine.
So I can now resize my VBox window nicely. Still struggling with guest
machine USB recognition, however. Not sure whether this is due to installing
Guest Additions manually, or if it's a more generic problem.
I use a program called Macrex for my job. It runs on Windows. Some
alternative software exists, but none of it runs in GNU/Linux. I'm not
confident with WINE, and don't think I'd trust it for mission-critical stuff
anyway. At the moment I'm dual-booting, but I'd prefer to keep Windows
confined to a VM.