[dotnet] Address warnings for Firefox devtool depreciations (#14786)

Author: RenderMichael

dotnet/src/webdriver/Firefox/FirefoxDriver.cs

@@ -393,6 +393,7 @@ public Screenshot GetFullPageScreenshot()
         /// Creates a session to communicate with a browser using the Chromium Developer Tools debugging protocol.
         /// </summary>
         /// <returns>The active session to use to communicate with the Chromium Developer Tools debugging protocol.</returns>
+        [Obsolete("CDP support for Firefox is deprecated and will be removed in future versions. Please switch to WebDriver BiDi.")]
         public DevToolsSession GetDevToolsSession()
         {
             return GetDevToolsSession(new DevToolsOptions() { ProtocolVersion = FirefoxDevToolsProtocolVersion });

dotnet/src/webdriver/Remote/RemoteWebDriver.cs

@@ -428,7 +428,7 @@ public ReadOnlyCollection<IWebElement> FindElementsByCssSelector(string cssSelec
         /// <returns>The active session to use to communicate with the Developer Tools debugging protocol.</returns>
         public DevToolsSession GetDevToolsSession()
         {
-            if (this.Capabilities.GetCapability(CapabilityType.BrowserName) == "firefox")
+            if (this.Capabilities.GetCapability(CapabilityType.BrowserName) is "firefox")
             {
                 if (_logger.IsEnabled(LogEventLevel.Warn))
                 {