--- a/mobile/android/base/java/org/mozilla/gecko/Tab.java
+++ b/mobile/android/base/java/org/mozilla/gecko/Tab.java
@@ -59,17 +59,17 @@ public class Tab {
     private IconRequestBuilder mIconRequestBuilder;
     private Future<IconResponse> mRunningIconRequest;
 
     private boolean mHasFeeds;
     private boolean mHasOpenSearch;
     private final SiteIdentity mSiteIdentity;
     private SiteLogins mSiteLogins;
     private BitmapDrawable mThumbnail;
-    private final int mParentId;
+    private volatile int mParentId;
     // Indicates the url was loaded from a source external to the app. This will be cleared
     // when the user explicitly loads a new url (e.g. clicking a link is not explicit).
     private final boolean mExternal;
     private boolean mBookmark;
     private int mFaviconLoadId;
     private String mContentType;
     private boolean mHasTouchListeners;
     private final ArrayList<View> mPluginViews;
@@ -163,16 +163,27 @@ public class Tab {
     public synchronized long getLastUsed() {
         return mLastUsed;
     }
 
     public int getParentId() {
         return mParentId;
     }
 
+    /**
+     * Updates the stored parent tab ID to a new value.
+     * Note: Calling this directly from Java currently won't update the parent ID value
+     * held by Gecko and the session store.
+     *
+     * @param parentId The ID of the tab to be set as new parent, or -1 for no parent.
+     */
+    public void setParentId(int parentId) {
+        mParentId = parentId;
+    }
+
     // may be null if user-entered query hasn't yet been resolved to a URI
     public synchronized String getURL() {
         return mUrl;
     }
 
     // mUserRequested should never be null, but it may be an empty string
     public synchronized String getUserRequested() {
         return mUserRequested;

--- a/mobile/android/base/java/org/mozilla/gecko/Tabs.java
+++ b/mobile/android/base/java/org/mozilla/gecko/Tabs.java
@@ -124,17 +124,19 @@ public class Tabs implements BundleEvent
             "Link:Favicon",
             "Link:Touchicon",
             "Link:Feed",
             "Link:OpenSearch",
             "DesktopMode:Changed",
             "Tab:StreamStart",
             "Tab:StreamStop",
             "Tab:AudioPlayingChange",
-            "Tab:MediaPlaybackChange");
+            "Tab:MediaPlaybackChange",
+            "Tab:SetParentId",
+            null);
 
         mPrivateClearColor = Color.RED;
 
     }
 
     public synchronized void attachToContext(Context context, LayerView layerView) {
         final Context appContext = context.getApplicationContext();
         if (mAppContext == appContext) {
@@ -600,16 +602,19 @@ public class Tabs implements BundleEvent
             } else if (event.equals("Tab:MediaPlaybackChange")) {
                 final String status = message.getString("status");
                 if (status.equals("resume")) {
                     notifyListeners(tab, TabEvents.MEDIA_PLAYING_RESUME);
                 } else {
                     tab.setIsMediaPlaying(status.equals("start"));
                     notifyListeners(tab, TabEvents.MEDIA_PLAYING_CHANGE);
                 }
+            } else if (event.equals("Tab:SetParentId")) {
+                int newParentId = message.getInt("parentID");
+                tab.setParentId(newParentId);
             }
 
         } catch (Exception e) {
             Log.w(LOGTAG, "handleMessage threw for " + event, e);
         }
     }
 
     public void refreshThumbnails() {

--- a/mobile/android/chrome/content/browser.js
+++ b/mobile/android/chrome/content/browser.js
@@ -3830,16 +3830,26 @@ Tab.prototype = {
           type: "Link:OpenSearch",
           tabID: this.id,
           visible: true
         });
       });
     }
   },
 
+  setParentId: function(aParentId) {
+    let newParentId = (typeof aParentId == "number") ? aParentId : -1;
+    this.parentId = newParentId;
+    Messaging.sendRequest({
+      type: "Tab:SetParentId",
+      tabID: this.id,
+      parentID: newParentId
+    });
+  },
+
   handleEvent: function(aEvent) {
     switch (aEvent.type) {
       case "DOMContentLoaded": {
         let target = aEvent.originalTarget;
 
         // ignore on frames and other documents
         if (target != this.browser.contentDocument)
           return;

--- a/mobile/android/components/SessionStore.js
+++ b/mobile/android/components/SessionStore.js
@@ -1479,17 +1479,18 @@ SessionStore.prototype = {
     let window = Services.wm.getMostRecentWindow("navigator:browser");
     for (let i = 0; i < aData.tabs.length; i++) {
       let tabData = JSON.parse(aData.tabs[i]);
       let isSelectedTab = (i == aData.tabs.length - 1);
       let params = {
         selected: isSelectedTab,
         isPrivate: tabData.isPrivate,
         desktopMode: tabData.desktopMode,
-        cancelEditMode: isSelectedTab
+        cancelEditMode: isSelectedTab,
+        parentId: tabData.parentId
       };
 
       let tab = window.BrowserApp.addTab(tabData.entries[tabData.index - 1].url, params);
       tab.browser.__SS_data = tabData;
       tab.browser.__SS_extdata = tabData.extData;
       this._restoreTab(tabData, tab.browser);
     }
   },
@@ -1631,33 +1632,38 @@ SessionStore.prototype = {
     log("restoreWindow() window.BrowserApp.selectedTab is " + window.BrowserApp.selectedTab.id);
 
     for (let i = 0; i < tabs.length; i++) {
       let tabData = tabs[i];
       let entry = tabData.entries[tabData.index - 1];
 
       // Use stubbed tab if we've already created it; otherwise, make a new tab
       let tab;
+      let parentId = tabData.parentId;
       if (tabData.tabId == null) {
         let params = {
           selected: (selected == i+1),
           delayLoad: true,
           title: entry.title,
           desktopMode: (tabData.desktopMode == true),
-          isPrivate: (tabData.isPrivate == true)
+          isPrivate: (tabData.isPrivate == true),
+          parentId: parentId
         };
         tab = window.BrowserApp.addTab(entry.url, params);
       } else {
         tab = window.BrowserApp.getTabForId(tabData.tabId);
 
         // Don't restore tab if user has closed it
         if (tab == null) {
           delete tabData.tabId;
           continue;
         }
+        if (parentId > -1) {
+          tab.setParentId(parentId);
+        }
       }
 
       tab.browser.__SS_data = tabData;
       tab.browser.__SS_extdata = tabData.extData;
 
       if (window.BrowserApp.selectedTab == tab) {
         this._restoreTab(tabData, tab.browser);
 
@@ -1718,17 +1724,18 @@ SessionStore.prototype = {
       }
     });
 
     // create a new tab and bring to front
     let params = {
       selected: true,
       isPrivate: aCloseTabData.isPrivate,
       desktopMode: aCloseTabData.desktopMode,
-      tabIndex: this._lastClosedTabIndex
+      tabIndex: this._lastClosedTabIndex,
+      parentId: aCloseTabData.parentId
     };
     let tab = aWindow.BrowserApp.addTab(aCloseTabData.entries[aCloseTabData.index - 1].url, params);
     tab.browser.__SS_data = aCloseTabData;
     tab.browser.__SS_extdata = aCloseTabData.extData;
     this._restoreTab(aCloseTabData, tab.browser);
 
     this._lastClosedTabIndex = -1;