Stop mouseup propagation while inspecting

src/backend/agent.js

@@ -320,6 +320,7 @@ export default class Agent extends EventEmitter {
   startInspectingDOM = () => {
     window.addEventListener('click', this._onClick, true);
     window.addEventListener('mousedown', this._onMouseDown, true);
+    window.addEventListener('mouseup', this._onMouseUp, true);
     window.addEventListener('mouseover', this._onMouseOver, true);
   };
 
@@ -339,6 +340,7 @@ export default class Agent extends EventEmitter {
 
     window.removeEventListener('click', this._onClick, true);
     window.removeEventListener('mousedown', this._onMouseDown, true);
+    window.removeEventListener('mouseup', this._onMouseUp, true);
     window.removeEventListener('mouseover', this._onMouseOver, true);
   };
 
@@ -408,6 +410,14 @@ export default class Agent extends EventEmitter {
     }
   };
 
+  // While we don't do anything here, this makes choosing
+  // the inspected element less invasive and less likely
+  // to dismiss e.g. a context menu.
+  _onMouseUp = (event: MouseEvent) => {
+    event.preventDefault();
+    event.stopPropagation();
+  };
+
   _onMouseOver = (event: MouseEvent) => {
     event.preventDefault();
     event.stopPropagation();