It sounds like you’re almost there! On some versions of the Firefox app, the “Ready to Scan” button doesn’t appear right away try closing the app completely and reopening it, then go to the menu → sign in again. Sometimes it only shows after a quick refresh. Also make sure your Firefox app is fully updated. I’ve done similar setups and keeping notes in Phonexa helped me track which devices were synced and avoid confusion. Once it shows, you should be able to scan the QR code and finish the login.