Could you post a Sync log to see if there is a problem?

You can check the about:sync-log page via the location/address bar to see if there are recent error logs available.

You can upload a recent log if the log is too big to put in a reply.

• http://pastebin.mozilla.org

https://pastebin.mozilla.org/8850565

This looks like a user name problem with loging in.

1445880926926   Sync.Status        DEBUG   Status.login: success.login => error.login.reason.no_username
1445880926926   Sync.Status        DEBUG   Status.service: success.status_ok => service.client_not_configured
1445880926926   Sync.Status        DEBUG   Status.login: error.login.reason.no_username => error.login.reason.no_username

In case of issues with Sync you can try this: Disconnect from Sync and Reconnect to Sync again. You can disconnect from Sync by clicking the e-mail address in the "3-bar" Firefox menu button drop-down list or go to "Options/Preferences > Sync". Delete the signedInUser.json file in the Firefox profile folder and delete the Weave folder (Sync was formerly named Weave). Remove an existing chrome://FirefoxAccounts entry in the Firefox Password Manager.

• Tools > Options > Security: Passwords: "Saved Passwords" > "Show Passwords"

If that isn't enough then delete the prefs.js files to reset all prefs and maybe also delete the compatibility.ini file to reinitialize the profile. Delete and re-create the FxA account or change the Sync password. Note that changing the Sync password will wipe all data stored on th Sync server. Make sure that you do not clear the passwords via "Clear History when Firefox closes"

You can use this button to go to the current Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)
• http://kb.mozillazine.org/Profile_folder_-_Firefox