Sync only sync between devices the original data is still on the main computer and that needs to be one for sync to sync properly between devices. If that is off and not accessible then the sync server will not update correctly for all the devices. And only way to restore that data from old computer to new is to do Firefox FAQ data migration steps and FAQ to restore them onto the new computer so they will remain there even if the other computer is no longer functional but the data will be on the new computer and not be lost. Remember sync isn't a backup system to backup to new computer requires to copy that data from old computer and import them to the new computer to preserve them on the new computer. Once the old is gone so will data and there so the sync server will not find or be able to sync between devices.

Hi George, does Chrome on Android sync data to your Google Account?

If so:

(1) Install Chrome on your Windows computer and sign it in to your Google account to download the data

(2) Then tell Firefox to import from Chrome on your computer. See: Import bookmarks and other data from Google Chrome

Does that work?

If you decide you want to uninstall Chrome from Windows after that, Firefox should not be affected. But unless you like Edge as your backup browser for sites that refuse to work correctly in Firefox, maybe just keep it??