Windows Live Mail is part of Windows Live Essentials

This program can be set to check for new mail however often you want.

Also, there is an add-on for Firefox that will also do what you want; Hotmail Watcher {web link}

Hotmail watcher seems to have disapeared from Mozilla, last year, apparently because it harms Firefox performance.

Sorry, a bit off-topic for this forum which is about Firefox questions. Firefox doesn't do email, it's strictly a web browser. We would be willing to try to help you if we knew what you were using for "email".

If your question is about Thunderbird a moderator can move this thread to the Thunderbird questions queue.

John99 said

Hotmail watcher seems to have disapeared from Mozilla, last year, apparently because it harms Firefox performance.

That's odd. Mine works fine. Found another link; https://sites.google.com/site/sonthakit/hotmailwatcher

That link is not to a Mozilla approved addon There is a strong possibility it could harm Firefox performance. Of course if Firefox is only being used to monitor email that is ok. But why use Firefox if that is all it is doing.

Additionlly, and almost certainly not in this instance, (The developer seems well respected, and with good intentions) un-approved addons have not had even a basic code review, and could have malware. Further in the in the near future signed addons are expected to be required for Firefox so if an addon is not reviewed by Mozilla and signed it will stop working with Firefox Relesases.