I setup a MS LifeCam HD3000 on a rev B rpi. It works decently well with the motion program. I currently stream 800x448 (modulo 16 safe) images of my outdoor aviary to home network and on the internet. While viewing the stream with Firefox 23, my 2 windows 7 PCs would sometimes crash after viewing for a while. Investigation with Task Manager and Resource Monitor on PC showed a chunk of memory was used up for every frame displayed in FF and wasn't returned to Windows OS. Eventually there's no "free" or "available" memory.
Memory leaks with FF have been a problem for a long time, but even current FF v.23.0.1 leaks memory when viewing mjpegs. The only way to recover memory is to close FF. To make sure I don't crash my Windows PCs, I set the motion.conf file webcam_limit to 180 frames, or about 3 minutes at 1 frame/sec. (I also observed iceweasel loosing memory on the rpi.) This works on my 2G netbook and 4G laptop.
see https://bugzilla.mozilla.org/show_bug.cgi?id=858615 for FF memory leak bug info.