Read this article. https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information

Thanks for the reply. Do you know from which address sync would send emails to a user from. I was searching through all my past emails that came from Mozilla, is this the same address as sync? Thanks again for reading

Assuming that all those other devices are connected to Sync prior to being upgraded to Firefox 29, you shouldn't need to mess around with your Sync key. The upgrade process from the old version of Sync to the new version is designed for minimal user involvement. The new version of Sync doesn't require the "Sync key / Recovery key", it uses a different type of encryption "key" that is derived from the account name and initial password, an is hidden from the user.

See this KB article - Sync your Firefox bookmarks, history, passwords and more

You shouldn't lose any data that is on the Sync server, and the data that is on the other PC's shouldn't be lost either.

@the_edmeister & @zoli62, Thanks both for the replies, I am still going to run into a problem of not knowing which of my email addresses I used to originally authenticate, if not today but looking into the future at some stage I will need this information. You could PM me if you think I am creating a security risk by knowing from where the email would have come from, this is what I would use to search all my emails from the past 10 or so years? Along the same lines of profile, what happens if I physically transport my Firefox profile folder (eg. %APPDATA%\Mozilla\Firefox\Profiles\xxxxxxxx.default\.) to another computer as this would circumvent the downloading from the server part of sync. But will it be update the browsing history etc? Thanks for reading.