EDIT 4: please try again with v4.0.80?

EDIT 3: we will take a look at Ghostery, thanks. Can you please say what your Ghostery settings are?

EDIT 2: can you say if you are running any other Firefox add-ons? Anything having to do with cookies or clearing private data? Also, please tell me if you have Content Blocking set higher than Standard in about:preferences#privacy. Could you please tell me the name of the board you're trying to save to? Is it a public or private board? (I thought it might be /my-digital-art/, but I can't find it anywhere in logs.)

EDIT: thanks for the links! I am able to save from both sites, but amandaclegg.co.uk is loading very slowly for me from San Francisco; what does your load time look like?

Sorry about that. Would you mind saying what OS (Mac, Windows) and version of Firefox you're using? Do you save to more than one Pinterest account? Can you please give me one or two URLs that are definitely not working for you right now, so I can try them out?