One other bit of subterfuge that also works is to hexedit (or even sed) /usr/lib/browser/libflashplayer.so and change /dev/video to /dev/v4lv1, then copy (and set permissions) from "/dev/video1" or whatever the loopback output is to "/dev/v4lv10". No LD_PRELOAD needed.

Camera and videocam work (when the flashcam app is NOT running and using the camera).

Note you need to have flashcam running before launching the page for flash to find the device. One of those status bar process runners works well (to start or killall flashcam).