diff --git a/browser/base/content/browser-fullZoom.js b/browser/base/content/browser-fullZoom.js
index 91ad06456fe..612e27902aa 100644
--- a/browser/base/content/browser-fullZoom.js
+++ b/browser/base/content/browser-fullZoom.js
@@ -439,9 +439,9 @@ var FullZoom = {
    * operations that access the given browser's zoom should use this method to
    * capture the token before starting and use token.isCurrent to determine if
    * it's safe to access the zoom when done.  If token.isCurrent is false, then
-   * the zoom of the browser was changed after the async operation started, and
-   * depending on what the operation is doing, it may no longer be safe to set
-   * the zoom or get it to then use in some manner.
+   * after the async operation started, either the browser's zoom was changed or
+   * the browser was destroyed, and depending on what the operation is doing, it
+   * may no longer be safe to set and get its zoom.
    *
    * @param browser  The token of this browser will be returned.
    * @return  An object with an "isCurrent" getter.
@@ -454,7 +454,12 @@ var FullZoom = {
     return {
       token: map.get(outerID),
       get isCurrent() {
-        return map.get(outerID) === this.token;
+        // At this point, the browser may have been destructed and unbound but
+        // its outer ID not removed from the map because outer-window-destroyed
+        // hasn't been received yet.  In that case, the browser is unusable, it
+        // has no properties, so return false.  Check for this case by getting a
+        // property, say, docShell.
+        return map.get(outerID) === this.token && browser.docShell;
       },
     };
   },