Please add a feature to manage number of active download. Make an option like "maximum number of simultaneous downloads" and then the user can choose certain number. If a user chooses "1" for that option, it will make FF to do one download at a time. So when there are more than one download item in the queue, FF will wait for the first single ongoing download to complete before starting the next one. I hope you devs will consider this. Maybe make it a test pilot experiment? Thanks!