fix: Don't open the toolbox when clicking beneath the categories

core/toolbox/toolbox.ts

@@ -108,6 +108,9 @@ export class Toolbox
   /** The workspace this toolbox is on. */
   protected readonly workspace_: WorkspaceSvg;
 
+  /** Whether the mouse is currently being clicked. */
+  private mouseDown = false;
+
   /** @param workspace The workspace in which to create new blocks. */
   constructor(workspace: WorkspaceSvg) {
     super();
@@ -243,6 +246,16 @@ export class Toolbox
     );
     this.boundEvents_.push(clickEvent);
 
+    const mouseUpEvent = browserEvents.bind(
+      container,
+      'pointerup',
+      this,
+      () => {
+        this.mouseDown = false;
+      },
+    );
+    this.boundEvents_.push(mouseUpEvent);
+
     const keyDownEvent = browserEvents.conditionalBind(
       contentsContainer,
       'keydown',
@@ -259,6 +272,7 @@ export class Toolbox
    * @param e Click event to handle.
    */
   protected onClick_(e: PointerEvent) {
+    this.mouseDown = true;
     if (browserEvents.isRightButton(e) || e.target === this.HtmlDiv) {
       // Close flyout.
       (common.getMainWorkspace() as WorkspaceSvg).hideChaff(false);
@@ -1134,7 +1148,10 @@ export class Toolbox
   ): void {
     if (node !== this) {
       // Only select the item if it isn't already selected so as to not toggle.
-      if (this.getSelectedItem() !== node) {
+      // Also require that the mouse not be down, i.e. that the focusing of
+      // the toolbox was keyboard-driven, to avoid opening the flyout when
+      // clicking on an empty part of the toolbox.
+      if (this.getSelectedItem() !== node && !this.mouseDown) {
         this.setSelectedItem(node as IToolboxItem);
       }
     } else {

tests/browser/test/toolbox_drag_test.mjs

@@ -207,4 +207,13 @@ suite('Open toolbox categories', function () {
     );
     await openCategories(this.browser, testCategories, screenDirection.RTL);
   });
+
+  test('clicking the toolbox itself does not open the flyout', async function () {
+    this.browser = await testSetup(testFileLocations.PLAYGROUND);
+    await this.browser.$('.blocklyToolbox').click();
+    const flyoutOpen = await this.browser.execute(() => {
+      return Blockly.getMainWorkspace().getFlyout().isVisible();
+    });
+    chai.assert.isFalse(flyoutOpen);
+  });
 });