Reflector can already open Silverlight xap files (and their dll contents) in at least 3 ways:

1. Open zip

   You do this by going to the file menu and choosing the Open Zip item (shown below) 

   Click on the Browse… button in the Open Zipped Assembly dialog.

   

   Make sure the Xap files filter is selected at the bottom of the Open File dialog

   

   This triggers the Open Zipped Assembly Dialog to popup with the contents of the Xap:

   

2. Drag a Xap file to the assembly tree

   You do this by just dragging a xap file to the Assembly tree in Reflector

   

   This triggers the Open Zipped Assembly Dialog to popup with the contents of the Xap:

   

3. Right click on a xap file (when Reflector is open)

   You should see the Browse with Reflector option on the context menu for a xap file (if not, you need to go to the command line, go to the directory your Reflector.exe is in and type "Reflector.exe /register")

   

   Once you click on the “Browse with .Net Reflector”, it will trigger the Open Zipped Assembly dialog with the contents of the xap like above.

   

Now there is a #4 - Right click on a xap file (when Reflector is NOT open)

With my new addin (download here: http://jasonhaley.com/files/Reflector.Silverlight.Opener.zip ), I added a shortcut that works if Reflector isn’t open and just adds all the dlls in the xap to the assembly tree.

So once you have the addin added to Reflector, the next time you want to open a xap file but don’t have Reflector open yet – just right click on the file and choose Browse with .NET Reflector and Reflector should open with all the dlls that were in the xap file added to the assembly tree.