Sorry, without access to the email account that you used when you set up Firefox Sync you're out of luck. Adding a 2nd email address at this time would require "approving" that change addition via an email which would be sent to that inaccessible email account. As far the password for your Sync account. if you don't remember it you could reset your password, but when that is done all data saved in Sync would be deleted. A different password would create a different security key which wouldn't be able to decrypt your saved data, rendering it an undecipherable "blob". What about another device connected to that Sync account? If you say that only one device was ever used with Sync, you weren't using Sync properly. It is not a "cloud" storage medium for storing Firefox data for a solitary device or for backup purposes. Its intended purpose is "synchronizing" Firefox user data across multiple devices. If you were using another device which still has your Firefox data, just create a new Firefox Account and start from scratch. https://support.mozilla.org/en-US/kb/access-mozilla-services-firefox-accounts