Bug 1358713, when a popup's anchor does not have a frame originally, don't have the popup update its position to follow it, r=tn

layout/xul/nsMenuPopupFrame.cpp

@@ -2510,11 +2510,13 @@ nsMenuPopupFrame::ShouldFollowAnchor(nsRect& aRect)
   }
 
   nsIFrame* anchorFrame = mAnchorContent->GetPrimaryFrame();
-  if (anchorFrame) {
-    nsPresContext* rootPresContext = PresContext()->GetRootPresContext();
-    if (rootPresContext) {
-      aRect = ComputeAnchorRect(rootPresContext, anchorFrame);
-    }
+  if (!anchorFrame) {
+    return false;
+  }
+
+  nsPresContext* rootPresContext = PresContext()->GetRootPresContext();
+  if (rootPresContext) {
+    aRect = ComputeAnchorRect(rootPresContext, anchorFrame);
   }
 
   return true;

toolkit/content/tests/chrome/window_panel_anchoradjust.xul

@@ -32,6 +32,9 @@
   <menuitem label="Three"/>
 </menupopup>
 
+<button id="anchorhidden" label="HiddenAnchor" hidden="true"/>
+<button id="anchorextra" label="ExtraAnchor"/>
+
 <script type="application/javascript"><![CDATA[
 
 Components.utils.import("resource://gre/modules/Task.jsm");
@@ -140,6 +143,27 @@ function runTests() {
     yield popuphidden;
     yield menupopuphidden;
 
+    // A popup with a hidden anchor should not update
+    let anchorhidden = document.getElementById("anchorhidden");
+    popupshown = waitForPanel(panel, "popupshown");
+    panel.openPopup(anchorhidden, "after_start");
+    yield popupshown;
+
+    let oldtop = panel.getBoundingClientRect().top;
+
+    // Show and adjust anchors. The panel should not update or hide due to this.
+    anchorhidden.hidden = false;
+    document.getElementById("anchorextra").hidden = true;
+    yield new Promise(r => { SimpleTest.executeSoon(r); });
+
+    let newtop = panel.getBoundingClientRect().top;
+    is(panel.state, "open", "panel is still open after showing anchor");
+    is(oldtop, newtop, "panel top did not change after showing anchor");
+
+    popuphidden = waitForPanel(panel, "popuphidden");
+    panel.hidePopup();
+    yield popuphidden;
+
     // The panel should no longer follow anchors.
     panel.setAttribute("followanchor", "false");