'''''"I signed up to Firefox years ago ..."''''' and '''''"Can't remember mail address or password to sync."''''' doesn't sound good. Use the 3-bar '''Open menu''' button on a Firefox installation that is connected to Sync. You'll see the email address that is connected to your Sync account where it would say '''Sign in to Sync''' if you're not signed in. If you don't currently have Firefox on a device that is signed in to Sync, but do have a device that was used with Sync - look to Saved Logins and you should see the email address that you used for Sync next to '''chrome://FirefoxAccounts(Firefox Account credentials)'''. But if you can't remember the Password that you used, you're screwed; the Password shown there is for internal Sync connection & authentication, and has the "dual kA & kB security keys" used by Firefox to automatically log in to the Sync server - that "password" can't be used by the user. If you truly forgot your Password your data on the SYnc server is useless; if it is still even present after an extended period of time. ----------------- Overall, it sounds like you were using Sync incorrectly. Sync isn't intended for long term storage of Firefox data from one device, it is intended to be used to synchronize Firefox data among multiple devices continuously as each device with Firefox connects to the internet real time. Long term retention of data where months or years of no user device connection to Sync has been made is unpredictable - IOW, that wasn't a design goal.