Prevent default on mouse down (fixes #64350)

src/vs/workbench/browser/parts/quickinput/quickInputList.ts

@@ -279,6 +279,12 @@ export class QuickInputList {
 					break;
 			}
 		}));
+		this.disposables.push(this.list.onMouseDown(e => {
+			if (e.browserEvent.button !== 2) {
+				// Works around / fixes #64350.
+				e.browserEvent.preventDefault();
+			}
+		}));
 		this.disposables.push(dom.addDisposableListener(this.container, dom.EventType.CLICK, e => {
 			if (e.x || e.y) { // Avoid 'click' triggered by 'space' on checkbox.
 				this._onLeave.fire();