Thunderbird cursor hover theme preview not working

In Firefox, if i browse themes, i can hover my mouse cursor over any theme and it instantly previews it for me. It used to do this in Thunderbird, just fine. Then one day i stopped. I have uninstalled and reinstalled Thunderbird. I have also in stalled the Beta 45.0 version. No dice. Please let me know what to do.

It could be related to add-ons you have installed or settings you have changed. There are some settings related to third-party cookies and third-party image loading that might be related.

I am running Thunderbird 78.10.0 (64-bit) with no add-ons, and the preview function is not working for me either.