Unable to open [object Object]

For about 2 weeks on my MacBook Pro, I've been unable to see and zoom in on images on the Library of Congress web site, e.g. https://www.loc.gov/resource/g3200.ct001471/

The error in the viewer is "Unable to open [object Object]: HTTP 0 Attempting to load TileSource"

The same error shows up no matter which of three web browsers I use (Safari, Chrome, Firefox).

However, I can see and zoom such images on my iPhone and on a PC, so it seems to be a new problem with my MacBook Pro and not with the Library of Congress web site. I think the problem may be temporally related to the last OS update, Sierra Version 10.12.2

Any ideas?