when trying to view pdf attachment while composing a thunderbird message a mysterious error message appears: "could not be opened, because the associated helper application does not exist. Change the association in your preferences". I found the solution in a reddit forum namely in configeditor of thunderbird change "pdfjs.disabled" to "true". Fine, but why does thunderbird support not give a solution?. And why is the error message so uninformative? it does not say which helper application it is looking for, and what is meant by "association in your preferences" and how to change that. SEE https://www.reddit.com/r/Thunderbird/comments/qrpmnb/cant_open_attachments_while_composing/