foo.rb

....
    def self.storage
      @storage ||= begin
         storage = Plugin::Storage.new('application_plugin')
         storage.set_default('stay_resident_after_last_window_closed', false)
         storage.set_default('show_toolbar', true)
         storage
      end
    end
....

....
   def initialize
      @windows = []
      @window_handlers = Hash.new {|h,k| h[k] = []}
      create_clipboard
      create_history
      @event_spewer = EventSpewer.new
      @task_queue   = TaskQueue.new
      @show_toolbar = !!Application.storage['show_toolbar']
    end
....

....
    def show_toolbar?
      @show_toolbar
    end

    def show_toolbar=(bool)
      Application.storage['show_toobar'] = @show_toolbar = bool
    end

    def toggle_show_toolbar
      Application.storage['show_toolbar'] = @show_toolbar = !Application.storage['show_toolbar']
    end
....