Issue 2878 - Element Hiding Helper is stuck in a bad state after a tab crash

lib/aardvark.js

 /*
  * This Source Code is subject to the terms of the Mozilla Public License
  * version 2.0 (the "License"). You can obtain a copy of the License at
  * http://mozilla.org/MPL/2.0/.
  */
 
 let {Prefs} = require("prefs");
 
 // Make sure to stop selection when we are uninstalled
 onShutdown.add(() => Aardvark.quit());
@@ skipping 235 matching lines @@
   {
     this.doCommand("quit", null);
   },
 
   onMouseMove: function(event)
   {
     this.mouseX = event.screenX;
     this.mouseY = event.screenY;
 
     this.hideSelection();
+    if (!this.browser)
+    {
+      // hideSelection() called quit()
+      return;
+    }
 
     let x = event.clientX;
     let y = event.clientY;
 
     // We might have coordinates relative to a frame, recalculate relative to top window
     let node = event.target;
     while (node && node.ownerDocument && node.ownerDocument.defaultView && node.ownerDocument.defaultView.frameElement)
     {
       node = node.ownerDocument.defaultView.frameElement;
       let rect = node.getBoundingClientRect();
@@ skipping 120 matching lines @@
     this.paintNode = doc.defaultView;
     if (this.paintNode)
     {
       this.prevPos = pos;
       this.paintNode.addEventListener("MozAfterPaint", this.onAfterPaint, false);
     }
   },
 
   hideSelection: function()
   {
-    if (this.boxElem.parentNode)
-      this.boxElem.parentNode.removeChild(this.boxElem);
+    try
+    {
+      if (this.boxElem.parentNode)
+        this.boxElem.parentNode.removeChild(this.boxElem);
+    }
+    catch (e)
+    {
+      // Are we using CPOW whose process is gone? Quit!
+      // Clear some variables to prevent recursion (quit will call us again).
+      this.boxElem = {};
+      this.paintNode = null;
+      this.quit();
+      return;
+    }
 
     if (this.paintNode)
       this.paintNode.removeEventListener("MozAfterPaint", this.onAfterPaint, false);
+
     this.paintNode = null;
     this.prevPos = null;
   },
 
   getWindowSize: function(wnd)
   {
     return [wnd.innerWidth, wnd.document.documentElement.clientHeight];
   },
 
   getElementPosition: function(element)
@@ skipping 350 matching lines @@
     // Show help box
     helpBox.showPopup(this.browser, -1, -1, "tooltip", "topleft", "topleft");
     return true;
   }
 }
 
 // Makes sure event handlers like Aardvark.onKeyPress always have the correct
 // this pointer set.
 for (let method of ["onMouseClick", "onMouseScroll", "onKeyPress", "onPageHide", "onMouseMove", "onAfterPaint", "quit"])
   Aardvark[method] = Aardvark[method].bind(Aardvark);