Hi John,
in theory you can specify all that parameters via the desired_capabilities in the open browser keyword.
In practice it only works for everything, like webdriver_assume_untrusted_issuer=true, except the proxy, because the proxy information is a nested object, and the parser of the Selenium2Library cannot handle that. See:
There is a kind of fall back solution that mostly works:.
If you are executing your tests with python, you can set the following environment variables:
http_proxy=http://<host>:<port>
HTTP_PROXY=http://<host>:<port>
If you are executing your tests with jython, you can set the following parameters:
Hope that helps somehow.
Queers,
Markus