For In-Browser Silverlight apps you need the following to make sure that you don’t get cross browser scripting errors:
Creating a test certificate for Xap file
I ran commands from a dos prompt to create the certificate, import it into MMC and then use VS 2010 to sign my Xap file
DOS commands for cert - I made my own root CA certificate;
Then I opened up MMC and went to the CurrentUser\Trusted Root Certification Authorities store and I imported mytestRootCA.cer file into that store
Then I made a signing certificate from that CA.
And that command line is installing that certificate into the personal store and it should be trusted because it chains up to the testRootCA.
I also needed to make sure that my signing certificate is also in my CurrentUser\Trusted Publishers store so I went back to MMC and import that certificate into that store (my file is called testSigning.cer).
Signing my Xap file with the new cert
From VS 2010 - Went to the Silverlight project properties and on the Signing area clicked on Select from Store and picked my certificate that was just created
Registry setting changes on client side