Avoid prematurely serializing the Proxy in FirefoxDriver

It'll be correctly converted to a json object and sent across
the wire, and the XPI was already half expecting a valid
object too.

Author: shs96c

java/client/src/org/openqa/selenium/firefox/FirefoxDriver.java

@@ -242,6 +242,7 @@ private static FirefoxOptions getFirefoxOptions(Capabilities capabilities) {
     if (marionette instanceof Boolean) {
       options.setLegacy(!(Boolean) marionette);
     }
+
     return options;
   }
 
@@ -302,7 +303,7 @@ private static Capabilities dropCapabilities(Capabilities capabilities) {
     // Ensure that the proxy is in a state fit to be sent to the extension
     Proxy proxy = Proxy.extractFrom(capabilities);
     if (proxy != null) {
-      caps.setCapability(PROXY, new BeanToJsonConverter().convert(proxy));
+      caps.setCapability(PROXY, proxy);
     }
 
     return caps;