How do I sync my phone and computer?

Both devices need to be signed in to the same Mozilla account; that's what links them. On the Mac: open the Firefox menu (three lines, top right), sign in to sync, and once signed in use "Connect another device" from the account menu. It shows a QR code. On the Android phone: open the Firefox menu (three dots), go to Settings, tap "Sync and save data", choose "Ready to scan" and point the camera at the QR code on the Mac. If you'd rather not scan, you can choose to sign in with email instead and use the same account. After that, check Settings > Sync on both devices to make sure bookmarks, history, passwords etc. are ticked, and give it a few minutes for the first sync. If you've already done this, what exactly happens: an error message, or both signed in but data not showing up?