--- a/browser/base/content/tabbrowser.xml
+++ b/browser/base/content/tabbrowser.xml
@@ -2498,19 +2498,39 @@
             let tabListener = this.mTabListeners[index];
             let ourBrowser = this.getBrowserForTab(aOurTab);
             ourBrowser.webProgress.removeProgressListener(filter);
             filter.removeProgressListener(tabListener);
 
             // Make sure to unregister any open URIs.
             this._swapRegisteredOpenURIs(ourBrowser, aOtherBrowser);
 
+            // Unmap old outerWindowIDs.
+            this._outerWindowIDBrowserMap.delete(ourBrowser.outerWindowID);
+            let remoteBrowser = aOtherBrowser.ownerDocument.defaultView.gBrowser;
+            if (remoteBrowser) {
+              remoteBrowser._outerWindowIDBrowserMap.delete(aOtherBrowser.outerWindowID);
+            }
+
             // Swap the docshells
             ourBrowser.swapDocShells(aOtherBrowser);
 
+            if (ourBrowser.isRemoteBrowser) {
+              // Switch outerWindowIDs for remote browsers.
+              let ourOuterWindowID = ourBrowser._outerWindowID;
+              ourBrowser._outerWindowID = aOtherBrowser._outerWindowID;
+              aOtherBrowser._outerWindowID = ourOuterWindowID;
+            }
+
+            // Register new outerWindowIDs.
+            this._outerWindowIDBrowserMap.set(ourBrowser.outerWindowID, ourBrowser);
+            if (remoteBrowser) {
+              remoteBrowser._outerWindowIDBrowserMap.set(aOtherBrowser.outerWindowID, aOtherBrowser);
+            }
+
             // Restore the progress listener
             this.mTabListeners[index] = tabListener =
               this.mTabProgressListener(aOurTab, ourBrowser, false);
 
             const notifyAll = Ci.nsIWebProgress.NOTIFY_ALL;
             filter.addProgressListener(tabListener, notifyAll);
             ourBrowser.webProgress.addProgressListener(filter, notifyAll);
           ]]>