I’ve been stuck on this for a few days.
At the moment, Firefox 3.6.4 (and newer) have a new functionality called ‘Crash protection’, which is quite nice.
It now runs the plugins in a separate process called ‘plugin-container.exe’ (look in your task manager).
But for developers it’s quite the hassle, since Visual Studio attaches itself to Firefox but NOT to this process. So no more Silverlight debugging for you!
Luckily there are two options for you!
The first option is the most straight forward, but has to be done each time. Use Visual Studio to attach itself to plugin-container.exe, refresh the website, and BAM, you’re up and running!
On the next screen click ‘plugin-container.exe’. There might be 2, if so, select the one with ‘Silverlight’ in the ‘Type’ column:
And hit ‘Attach’.
While this solution is adequate for when you need to debug it one time at a day, but for me, I only debug in Firefox, and when necessary I use Internet Explorer. For that you can go to your ‘about:config’ in Firefox, disable ‘dom.ipc.plugins.enabled.npctrl.dll’ (set it to false).