Motion stops streaming on movement (and no logs produced)

I am trying to get a hello-world stream working from a USB webcam to a browser over a local network using Motion. (On a Raspberry Pi). When I run service motion start on the RPi and go to http://192.168.0.xyz:8081 on my PC, the streaming works as expected. But when there is any movement, in Firefox it stops and says "Connection was reset". Refreshing sometimes makes it work, but sometimes gives a "Could not connect" message. In chrome the picture just freezes. I am not trying to use any motion-detection features for the moment, and have disabled all such options (that I have found). cat /tmp/motion.log is empty. Installation was as follows. (Everything was done as root to make things a bit simpler.) apt-get update apt-get install motion -y I then changed the following options in /etc/motion/motion.conf daemon off setup_mode off output_pictures off output_debug_pictures off target_dir /var/lib/motion stream_port 8081 stream_motion off stream_localhost off Then I run service motion start What am I doing wrong?