Dispose of newly-instantiated Forms when populating Tool Box

see #2741, fe6bf7ba1, #2763

src/BizHawk.Client.EmuHawk/tools/ToolBox.cs

@@ -59,21 +59,21 @@ namespace BizHawk.Client.EmuHawk
 
 			foreach (var t in tools)
 			{
-				var instance = Activator.CreateInstance(t);
-
+				var wasLoaded = Tools.Has(t);
+				var instance = (Form) Tools.Load(t, focus: false);
 				var tsb = new ToolStripButton
 				{
-					Image = ((Form) instance).Icon.ToBitmap(),
-					Text = ((Form) instance).Text,
-					DisplayStyle = ((Form) instance).ShowIcon ? ToolStripItemDisplayStyle.Image : ToolStripItemDisplayStyle.Text
+					Image = instance.Icon.ToBitmap(),
+					Text = instance.Text,
+					DisplayStyle = instance.ShowIcon ? ToolStripItemDisplayStyle.Image : ToolStripItemDisplayStyle.Text
 				};
-
+				if (!wasLoaded) instance.Dispose();
 				tsb.Click += (o, e) =>
 				{
-					Tools.Load(t);
+					if (wasLoaded) instance.Focus(); // instance refers to already opened tool, focus it
+					else Tools.Load(t); // instance was new and has been disposed by now
 					Close();
 				};
-
 				ToolBoxStrip.Items.Add(tsb);
 			}
 		}

src/BizHawk.Client.EmuHawk/tools/ToolManager.cs

@@ -487,6 +487,11 @@ namespace BizHawk.Client.EmuHawk
 			return _tools.Any(t => t is T && t.IsActive);
 		}
 
+		/// <returns><see langword="true"/> iff a tool of the given <paramref name="toolType"/> is <see cref="IToolForm.IsActive">active</see></returns>
+		public bool Has(Type toolType)
+			=> typeof(IToolForm).IsAssignableFrom(toolType)
+				&& _tools.Any(t => toolType.IsInstanceOfType(t) && t.IsActive);
+
 		/// <summary>
 		/// Gets the instance of T, or creates and returns a new instance
 		/// </summary>