ruby: Ensure Firefox capabilities are proper instance by default

Signed-off-by: Alexei Barantsev <[email protected]>

Author: p0deje

Diff for: rb/lib/selenium/webdriver/firefox/bridge.rb

@@ -28,7 +28,7 @@ def initialize(opts = {})
           http_client = opts.delete(:http_client)
           proxy       = opts.delete(:proxy)
 
-          caps = opts.delete(:desired_capabilities) || {}
+          caps = opts.delete(:desired_capabilities) { Remote::Capabilities.firefox }
 
           @launcher = create_launcher(port, profile)