I am using Wiindows 7 Starter. Hotmail has suddenly started duplicatiing all emails received. Only the sender is duplicated and cannot be deleted without the actual email.
How can Stop these duplication because it fills up my inbox
This does not sound like an issue with Firefox, but is something that the Hotmail support team should be able to help you with.
There's a link for that on this page: https://support.mozilla.org/en-US/kb/problems-with-email-how-to-find-help