I'm afraid that is the only way to restore favicons. Favicons aren't stored as part of Sync data and will be lost. Note that only an HTML backup includes favicon, even restoring a JSON backup will lead to the loss of favicons. You can start with the bookmarks you use most frequently and the ones that show on the Bookmarks Toolbar. You can fill in the other at a later time. Keep in m,ind that Sync isn't meant to be used as a backup device and you might lose all your personal data in case something goes wrong and you do not have a local backup. *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles