I've got a windows 10 15inch screen laptop.
I've tried firefox, chrome and edge. The 'problem' exists for all 3.
I've resorted to downloading the image from the much bigger button in the top middle of the image, clicking the open option rather than save, and can then decide later if I want to save it to my computer.
I've also sent an email registering my complaint to FindMyPast, via their contact us option at the bottom of the site pages. Live chat unfortunately wasn't working today.
Maybe a flurry of complaint emails will make them see there is an issue