Did you contact them about this issue. Some sites will block image or video saving for their site security. So maybe it work back then but they change security so that ine can't save images or videos.

I spoke to Ancestry & they said it's not their fault. I tried with Edge (which I hate), & it worked fine, so it does seem to be a Firefox problem

Unless one can provide screenshot error or crash reporting and or steps to replicate the issue no one will know what is going on. And since that is a login site unless a registered user can only verify the issue. Did you ask their help to try from Firefox to verify they get the same issue.