webcam not working anymore
I found out that the camera is taken over, somehow, by the google talk browser plugin. I solved by doing the following. From a terminal, I issued the following command

ps uaxw |grep Firefox


It will show a list of the processes under Firefox. One of them may be something like

sbo      21173   0.0  0.1   414040   2492   ??  S     5May11   0:07.47 
   /Applications/Firefox.app/Contents/MacOS/plugin-container.app/Contents/
   MacOS/plugin-container /Library/Internet Plug-Ins/googletalkbrowserplugin.plugin
   -omnijar /Applications/Firefox.app/Contents/MacOS/omni.jar 21168 
   gecko-crash-server-pipe.21168 org.mozilla.machname.855559451 plugin


I wrapped the long line. I then proceeded to kill this process (the pid is the first number)

  kill 21173


and the iSight started working again.