Bug 1159301, clear the mouse capture whenever a menu is opened, r=tn

browser/base/content/test/general/browser_selectpopup.js

@@ -416,3 +416,32 @@ add_task(function* test_large_popup() {
 
   yield BrowserTestUtils.removeTab(tab);
 });
+
+// This test checks that a mousemove event is fired correctly at the menu and
+// not at the browser, ensuring that any mouse capture has been cleared.
+add_task(function* test_mousemove_correcttarget() {
+  const pageUrl = "data:text/html," + escape(PAGECONTENT_SMALL);
+  let tab = yield BrowserTestUtils.openNewForegroundTab(gBrowser, pageUrl);
+
+  let selectPopup = document.getElementById("ContentSelectDropdown").menupopup;
+
+  let popupShownPromise = BrowserTestUtils.waitForEvent(selectPopup, "popupshown");
+  yield BrowserTestUtils.synthesizeMouseAtCenter("#one", { type: "mousedown" }, gBrowser.selectedBrowser);
+  yield popupShownPromise;
+
+  yield new Promise(resolve => {
+    window.addEventListener("mousemove", function checkForMouseMove(event) {
+      window.removeEventListener("mousemove", checkForMouseMove, true);
+      is(event.target.localName.indexOf("menu"), 0, "mouse over menu");
+      resolve();
+    }, true);
+
+    EventUtils.synthesizeMouseAtCenter(selectPopup.firstChild, { type: "mousemove" });
+  });
+
+  yield BrowserTestUtils.synthesizeMouseAtCenter("#one", { type: "mouseup" }, gBrowser.selectedBrowser);
+
+  yield hideSelectPopup(selectPopup);
+
+  yield BrowserTestUtils.removeTab(tab);
+});

layout/xul/nsMenuPopupFrame.cpp

@@ -852,8 +852,8 @@ nsMenuPopupFrame::ShowPopup(bool aIsContextMenu)
     mPopupState = ePopupOpening;
     mIsOpenChanged = true;
 
-    // Clear mouse capture when a context menu is opened.
-    if (aIsContextMenu) {
+    // Clear mouse capture when a popup is opened.
+    if (mPopupType == ePopupTypeMenu) {
       nsIPresShell::SetCapturingContent(nullptr, 0);
     }