I try to answer your questions. Correct me if I should not have understood you correctly.
At this time there is no support for browser specific network/proxy configuration. Also the marionette capability is not covered by Multi-Browser-Suite. Anyway you can try to advance the code with your own that fits your needs.
You could change the code in the createWebdriver function of class AnnotationRunnerHelper. Your modifications would look like this but it would affect all Firefox configurations.
else if (firefoxBrowsers.contains(browserName))
FirefoxProfile profile = new FirefoxProfile();
return new FirefoxDriver(capabilities);
I guess that you receive errors during lookup page elements. In that case you can use the implicite wait property. With that property you tell the WebDriver to wait up to x milli seconds to find the element before it will fail.
Another option would be the usage of the commandRetries property.
###The WebDriver’s implicit wait timeout [ms] used when finding elements. Defaults to 1000 ms.
com.xceptance.xlt.scripting.defaultImplicitWaitTimeout = 1000
How often to retry a command in case the target element was reported as stale. Defaults to 1.
com.xceptance.xlt.scripting.commandRetries = 1
Maybe you should also have a look on the waiting commands. These are a straight forward to use and you do not need separate pause commands.
I would need more information to help you in that case. I can not reproduce that behaviour.