maybe this will fix it?

lib/persistent_selenium/browser.rb

@@ -25,7 +25,7 @@ module PersistentSelenium
     end
 
     def set_app_host(host)
-      @app_host = host
+      @app_host = host.dup
 
       browser.navigate.to("data:text/html;base64,#{Base64.encode64(starting_page)}")
     end

lib/persistent_selenium/driver.rb

@@ -4,7 +4,7 @@ Capybara.register_driver :persistent_selenium do |app|
   require 'drb'
 
   DRb.start_service
-  browser = DRbObject.new nil, PersistentSelenium.url 
+  browser = DRbObject.new nil, PersistentSelenium.url
 
   server = Capybara::Server.new(app)
   server.boot