Kevin, thank you for supplying screenshots and all the additional information. (However, you might consider not posting your phone number publicly...) I suspect I know exactly what's causing this. Are you using AVG or Avast anti-virus? What you're experiencing could be a known issue caused by the anti-virus program's "Mail Shield" component. The developers are aware of it and have recently issued a beta test with a solution that ''should'' fix this. In the meantime, here's a support article from us that provides more information and potential workarounds to fix the issue: [[https://support.mozilla.org/en-US/questions/1384853]] Please let us know if the solutions there solve your problem!