There is a very long thread here in the forum on this problem. One possible cause is your proxy settings. If you check this deeply buried dialog, you may be able to correct it: orange Firefox button ''or'' classic Tools menu > Options > Advanced > Network Click the "Settings" button and choose either "No Proxy" or "Use System Settings" option, and OK the change. See whether that helps. More suggestions here: https://support.mozilla.org/en-US/questions/928922#answer-339570