More robust next tab selection after closing an active tab

app/browser/activeTabHistory.js

@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+* License, v. 2.0. If a copy of the MPL was not distributed with this file,
+* You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// static
+const activeTabsByWindow = new Map()
+
+const api = {
+  /**
+   * Inform this store that a tab is active for a window.
+   * This information will be added to index 0 in the
+   * active-tab history for the window.
+   */
+  setActiveTabForWindow: function (windowId, tabId) {
+    const existing = activeTabsByWindow.get(windowId)
+    if (existing) {
+      existing.unshift(tabId)
+    } else {
+      activeTabsByWindow.set(windowId, [ tabId ])
+    }
+  },
+
+  /**
+   * Retrieve the tabId that was active at the specified history index,
+   * 0 for most recent (default)
+   */
+  getActiveTabForWindow: function (windowId, historyIndex = 0) {
+    // get history of active tabs for specified window
+    const windowActiveTabs = activeTabsByWindow.get(windowId)
+    // handle no history for specified window
+    if (!windowActiveTabs || !windowActiveTabs.length) {
+      return null
+    }
+    // verify specified index in active-tab history exists
+    const lastIndex = windowActiveTabs.length - 1
+    if (lastIndex < historyIndex) {
+      return null
+    }
+    // get tabId at specified index in active-tab history
+    return windowActiveTabs[historyIndex]
+  },
+
+  /**
+   * Removes specified tab from active-tab history in specified window
+   */
+  clearTabFromWindow: function (windowId, tabId) {
+    const windowActiveTabs = activeTabsByWindow.get(windowId)
+    if (windowActiveTabs && windowActiveTabs.length) {
+      activeTabsByWindow.set(windowId, windowActiveTabs.filter(previousTabId => previousTabId !== tabId))
+    }
+  },
+
+  /**
+   * Forget history of active tabs for specified window
+   */
+  clearTabbedWindow: function (windowId) {
+    activeTabsByWindow.delete(windowId)
+  }
+}
+
+module.exports = api

app/browser/reducers/tabsReducer.js

@@ -201,8 +201,6 @@ const tabsReducer = (state, action, immutableAction) => {
         if (tabId === tabState.TAB_ID_NONE) {
           break
         }
-        const nextActiveTabId = tabs.getNextActiveTab(state, tabId)
-
         // Must be called before tab is removed
         // But still check for no tabId because on tab detach there's a dummy tabId
         const tabValue = tabState.getByTabId(state, tabId)
@@ -211,11 +209,6 @@ const tabsReducer = (state, action, immutableAction) => {
           state = tabs.updateTabsStateForWindow(state, windowIdOfTabBeingRemoved)
         }
         state = tabState.removeTabByTabId(state, tabId)
-        setImmediate(() => {
-          if (nextActiveTabId !== tabState.TAB_ID_NONE) {
-            tabs.setActive(nextActiveTabId)
-          }
-        })
         tabs.forgetTab(tabId)
       }
       break