The site http://www.stickam.com uses a Flash app to stream your webcam. I was only able to get my iSight webcam working in Chrome, not on Firefox or Safari. That was with version 10.0.3 flash I believe.
I upgraded my Flash to the latest version just now, and immediately my Safari cam worked, Firefox still doesn't, and Chrome stopped working. This without any other changes to my system.
In all three browsers I already have the flash permissions set to "allow" and it set to USB video, which is the correct setting for iSight.
Only thing I can think is this is a compatibility bug in the new version of Flash. Can anyone confirm this, or suggest anything else here?