There are a few ways to setup ssl in mono. For a full list or if you need finer grain control over trusted domains see Mono Security FAQ.
To use the root certificates trusted by Firefox you can use the mozroots tool included in
mono. You will need to connect the Edison modual to the internet through a wirless internet
connection. The command configure_edison --wifi will step you through connecting to
a wireless router. If you input a bad password or had to abort the wifi setup for any reason a
reboot may be required after configuration is complete to establish a connection.
Now run the command /mono/bin/mozroots --import --ask-remove and your done! You should
now be able to connect to secure websites as you would on any other .net platform.