                 read_only             : true
             @worksheet = new (sagews.SynchronizedWorksheet)(@view_doc, opts0)
 
-        if @ext == 'ipynb2'
+        if @ext == 'ipynb' and @jupyter_classic()
             @view_doc.once 'ready', =>
                 @view_doc.element.find(".smc-jupyter-notebook-buttons").hide()
                 @show()

                alert_message(type:'error', message:"Failed to open history document -- #{err}")
        )

    init_paths: =>
        #   @filename = "path/to/.file.sage-history"
        s = misc.path_split(@filename)

        opts.read_only = true
        switch @ext
            when 'ipynb'
                if @jupyter_classic()
                    @view_doc = jupyter.jupyter_notebook(@, @_open_file_path, opts).data("jupyter_notebook")
                    @element.find("a[href=\"#show-diff\"]").hide()
                else
                    @view_doc = jupyter_history_viewer_jquery_shim(@syncstring)
                    @element.find("a[href=\"#show-diff\"]").hide()
            when 'tasks'
                @view_doc = tasks.task_list(undefined, undefined, {viewer:true}).data('task_list')
                @element.find("a[href=\"#show-diff\"]").hide()
