The email address has been used as the "username" for Sync for a long time. The previously allowed "user name" like you mentioned has been long since discontinued - as of Firefox 29.

Check your Saved Passwords on another device for chrome://FirefoxAccounts (Firefox Accounts credentials) for the "Username" email address for your Sync account.

It might got discontinued long back.....but now i want my data(mail,bookmarks,password information) to be synced back to my emailid [pratap999@gmail.com]....Please help..

-Pratap.

Sorry, there is no way to access your data other than thru the Sync service. If you don't remember the email address that you used when signing up for Sync, try all the email addresses that you were using at that time - but if that was prior to Firefox 4.0 with the older (yet) Weave service, that won't work either. Overall, there were 2 major changes made to the Sync login information over the years - one that happened 4 months before Sync was built into Firefox 4.0 and the other with Firefox 29.

And if you don't have a 2nd device connected to that Sync account where you can retrieve that information from, you were using Sync incorrectly - it's not intended to be used as a "cloud" for storing data for one device.