I'm having this exact same problem. Any web pages that use Flash to access the webcam cause the plugin to crash.
Running firefox in terminal got me this (the webpage loaded but flash crashed):
However, libvdpau_nvidia.so appears to be present.
alex@kubuntu:~$ firefox www.testwebcam.com
2.4+ kernel w/o ELF notes? -- report this
Failed to open VDPAU backend libvdpau_nvidia.so: cannot open shared object file: No such file or directory
This is especially frustrating for me because I can't access any video sites through Linux, and VirtualBox doesn't have access to the webcam hardware so I can't run it in Windows either, and I'm not willing to duel boot just for webcam access.
alex@kubuntu:~$ locate libvdpau_nvidia.so
I'm using Chromium 23.0.1271.1 Ubuntu 12.10 and Mozilla Firefox 16.0.2 with Shockwave Flash 11.2 r202 on Kubuntu 12.10.