If an editor window breaks (due to an issue with serialized internal state for example) it can be a pain to close and reopen it as the context menu for closing it no longer works. This utility allows you to close any editor window.

WindowKiller.cs

// MIT License
// 
// Copyright (c) 2019 Sabresaurus
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

using UnityEngine;
using UnityEditor;

/// <summary>
/// If an editor window breaks (due to an issue with serialized internal state for example) it can be a pain to close and reopen it as the context menu for closing it no longer works. This utility allows you to close any editor window.
/// </summary>
public class WindowKiller : EditorWindow
{
    Vector2 scrollPosition = Vector2.zero;

    [MenuItem("Window/Window Killer")]
    public static void CreateAndShow()
    {
        EditorWindow window = EditorWindow.GetWindow<WindowKiller>(true, "Window Killer");

        window.Show();
    }

    private void OnGUI()
    {
        scrollPosition = EditorGUILayout.BeginScrollView(scrollPosition);

        EditorWindow[] openWindows = Resources.FindObjectsOfTypeAll<EditorWindow>();

        for (int i = 0; i < openWindows.Length; i++)
        {
            if(GUILayout.Button("Force Close " + openWindows[i].GetType().Name))
            {
                openWindows[i].Close();
            }
        }

        EditorGUILayout.EndScrollView();
    }
}