Updating .NET FirefoxDriver constructor for ICapabilities.

This allows the user to pass an ICapabilities object to the Firefox driver
constructor and have specific capabilities used in driver instantiation.
Fixes issue #6870.

Author: jimevans

dotnet/src/webdriver/Firefox/FirefoxDriver.cs

@@ -137,7 +137,7 @@ public FirefoxDriver(FirefoxProfile profile) :
         /// <param name="capabilities">The <see cref="ICapabilities"/> object containing the desired
         /// capabilities of this FirefoxDriver.</param>
         public FirefoxDriver(ICapabilities capabilities)
-            : this(ExtractBinary(capabilities), ExtractProfile(capabilities))
+            : this(ExtractBinary(capabilities), ExtractProfile(capabilities), capabilities, RemoteWebDriver.DefaultCommandTimeout)
         {
         }
 
@@ -162,7 +162,12 @@ public FirefoxDriver(FirefoxBinary binary, FirefoxProfile profile)
         /// to be used in starting Firefox.</param>
         /// <param name="commandTimeout">The maximum amount of time to wait for each command.</param>
         public FirefoxDriver(FirefoxBinary binary, FirefoxProfile profile, TimeSpan commandTimeout)
-            : base(CreateExtensionConnection(binary, profile, commandTimeout), DesiredCapabilities.Firefox())
+            : this(binary, profile, DesiredCapabilities.Firefox(), commandTimeout)
+        {
+        }
+
+        private FirefoxDriver(FirefoxBinary binary, FirefoxProfile profile, ICapabilities capabilities, TimeSpan commandTimeout)
+            : base(CreateExtensionConnection(binary, profile, commandTimeout), RemoveUnneededCapabilities(capabilities))
         {
             this.binary = binary;
             this.profile = profile;
@@ -345,6 +350,14 @@ private static ExtensionConnection CreateExtensionConnection(FirefoxBinary binar
             ExtensionConnection extension = new ExtensionConnection(binary, profileToUse, "localhost", commandTimeout);
             return extension;
         }
+
+        private static ICapabilities RemoveUnneededCapabilities(ICapabilities capabilities)
+        {
+            DesiredCapabilities caps = capabilities as DesiredCapabilities;
+            caps.Capabilities.Remove(FirefoxDriver.ProfileCapabilityName);
+            caps.Capabilities.Remove(FirefoxDriver.BinaryCapabilityName);
+            return caps;
+        }
         #endregion
     }
 }