diff --git a/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.dtd b/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.dtd
index 6ca3a82ed2f..d8f6db2f3b7 100644
--- a/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.dtd
+++ b/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.dtd
@@ -67,12 +67,22 @@
 <!ENTITY cmd.cancelUninstall.label        "Cancel Uninstall">
 <!ENTITY cmd.cancelUninstall.accesskey    "C">
 <!ENTITY cmd.cancelUninstall.tooltip      "Cancel the uninstall of this Add-on">
+<!ENTITY cmd.cancelInstall.label          "Cancel Install">
+<!ENTITY cmd.cancelInstall.accesskey      "C">
+<!ENTITY cmd.cancelInstall.tooltip        "Cancel the install of this Add-on">
+<!ENTITY cmd.cancelUpgrade.label          "Cancel Upgrade">
+<!ENTITY cmd.cancelUpgrade.accesskey      "C">
+<!ENTITY cmd.cancelUpgrade.tooltip        "Cancel the upgrade of this Add-on">
 <!ENTITY cmd.installUpdate.label          "Install Update">
 <!ENTITY cmd.installUpdate.accesskey      "I">
 <!ENTITY cmd.installUpdate.tooltip        "Install an update for this Add-on">
 <!-- The selected add-on's cancel action button label -->
 <!ENTITY cancel.label                     "Cancel">
 <!ENTITY cancel.accesskey                 "C">
+<!ENTITY cancelInstall.label              "Cancel">
+<!ENTITY cancelInstall.accesskey          "C">
+<!ENTITY cancelUpgrade.label              "Cancel">
+<!ENTITY cancelUpgrade.accesskey          "C">
 
 <!-- Only displayed in the selected Add-on's context menu -->
 <!ENTITY cmd.homepage.label               "Visit Home Page">
diff --git a/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties b/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties
index de5a892f018..73a380f9348 100644
--- a/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties
+++ b/mozilla/toolkit/locales/en-US/chrome/mozapps/extensions/extensions.properties
@@ -27,6 +27,14 @@ moreInfoText=More information
 uninstallTitle=Uninstall %S
 uninstallWarnDependMsg=%S is required by one or more add-ons. If you continue, the following items will be disabled:
 uninstallQueryMessage=Do you want to uninstall %S?
+cancelInstallTitle=Cancel Install of %S
+cancelInstallQueryMessage=Are you sure you want to cancel the install of %S?
+cancelInstallButton=Yes
+cancelCancelInstallButton=No
+cancelUpgradeTitle=Cancel Upgrade of %S
+cancelUpgradeQueryMessage=Are you sure you want to cancel the upgrade of %S?
+cancelUpgradeButton=Yes
+cancelCancelUpgradeButton=No
 disableTitle=Disable %S
 disableWarningDependMessage=If you disable %S, the following items that require this extension will also be disabled:
 disableQueryMessage=Do you want to disable %S?
diff --git a/mozilla/toolkit/mozapps/extensions/content/extensions.js b/mozilla/toolkit/mozapps/extensions/content/extensions.js
index 6a3d7e0455c..75c276ac877 100644
--- a/mozilla/toolkit/mozapps/extensions/content/extensions.js
+++ b/mozilla/toolkit/mozapps/extensions/content/extensions.js
@@ -1130,7 +1130,8 @@ function onAddonSelect(aEvent)
 // View Context Menus
 var gAddonContextMenus = ["menuitem_useTheme", "menuitem_options", "menuitem_homepage",
                           "menuitem_about",  "menuseparator_1", "menuitem_uninstall",
-                          "menuitem_cancelUninstall", "menuitem_checkUpdate",
+                          "menuitem_cancelUninstall", "menuitem_cancelInstall",
+                          "menuitem_cancelUpgrade", "menuitem_checkUpdate",
                           "menuitem_enable", "menuitem_disable"];
 var gUpdateContextMenus = ["menuitem_homepage", "menuitem_about", "menuseparator_1",
                            "menuitem_installUpdate", "menuitem_includeUpdate"];
@@ -1174,11 +1175,17 @@ function buildContextMenu(aEvent)
   var name = selectedItem ? selectedItem.getAttribute("name") : "";
   menuitem_about.setAttribute("label", getExtensionString("aboutAddon", [name]));
 
-  // When performing update or install tasks we don't support uninstall
+  /* When an update or install is pending allow canceling the update or install
+     and don't allow uninstall. When an uninstall is pending allow canceling the
+     uninstall.*/
   if (gView != "updates" && gView != "installs") {
     var canEnable = gExtensionsViewController.isCommandEnabled("cmd_cancelUninstall");
     document.getElementById("menuitem_cancelUninstall_clone").hidden = !canEnable;
-    document.getElementById("menuitem_uninstall_clone").hidden = canEnable;
+    var canCancelInstall = gExtensionsViewController.isCommandEnabled("cmd_cancelInstall");
+    document.getElementById("menuitem_cancelInstall_clone").hidden = !canCancelInstall;
+    var canCancelUpgrade = gExtensionsViewController.isCommandEnabled("cmd_cancelUpgrade");
+    document.getElementById("menuitem_cancelUpgrade_clone").hidden = !canCancelUpgrade;
+    document.getElementById("menuitem_uninstall_clone").hidden = canEnable || canCancelInstall || canCancelUpgrade;
   }
 
   switch (gView) {
@@ -1200,16 +1207,16 @@ function buildContextMenu(aEvent)
     document.getElementById("menuitem_options_clone").hidden = true;
     document.getElementById("menuitem_disable_clone").hidden = true;
     break;
-  case "locales":
   case "plugins":
+    document.getElementById("menuitem_about_clone").hidden = true;
+    document.getElementById("menuitem_uninstall_clone").hidden = true;
+    document.getElementById("menuitem_checkUpdate_clone").hidden = true;
+  case "locales":
     canEnable = gExtensionsViewController.isCommandEnabled("cmd_reallyEnable");
     document.getElementById("menuitem_enable_clone").hidden = !canEnable;
     document.getElementById("menuitem_disable_clone").hidden = canEnable;
     document.getElementById("menuitem_useTheme_clone").hidden = true;
     document.getElementById("menuitem_options_clone").hidden = true;
-    document.getElementById("menuitem_about_clone").hidden = true;
-    document.getElementById("menuitem_uninstall_clone").hidden = true;
-    document.getElementById("menuitem_checkUpdate_clone").hidden = true;
     break;
   case "updates":
     var includeUpdate = document.getAnonymousElementByAttribute(selectedItem, "anonid", "includeUpdate");
@@ -1597,6 +1604,27 @@ function closeEM() {
   closeWindow(true);
 }
 
+function confirmOperation(aName, aTitle, aQueryMsg, aAcceptBtn, aCancelBtn,
+                          aWarnMsg, aDependantItems) {
+  var params = {
+    message2: getExtensionString(aQueryMsg, [aName]),
+    title: getExtensionString(aTitle, [aName]),
+    buttons: {
+      accept: { label: getExtensionString(aAcceptBtn) },
+      cancel: { label: getExtensionString(aCancelBtn), focused: true }
+    }
+  }
+  if (aDependantItems.length > 0)
+    params.message1 = getExtensionString(aWarnMsg, [aName]);
+  var names = [];
+  for (var i = 0; i < aDependantItems.length; ++i)
+    names.push(aDependantItems[i].name + " " + aDependantItems[i].version);
+
+  window.openDialog("chrome://mozapps/content/extensions/list.xul", "", 
+                    "titlebar,modal,centerscreen", names, params);
+  return params.result == "accept";
+}
+
 var gExtensionsViewController = {
   supportsCommand: function (aCommand)
   {
@@ -1643,6 +1671,10 @@ var gExtensionsViewController = {
              !gExtensionsView.hasAttribute("update-operation");
     case "cmd_cancelUninstall":
       return selectedItem.opType == OP_NEEDS_UNINSTALL;
+    case "cmd_cancelInstall":
+      return selectedItem.opType == OP_NEEDS_INSTALL;
+    case "cmd_cancelUpgrade":
+      return selectedItem.opType == OP_NEEDS_UPGRADE;
     case "cmd_checkUpdate":
       return selectedItem.getAttribute("updateable") != "false" &&
              !gExtensionsView.hasAttribute("update-operation");
@@ -1829,24 +1861,10 @@ var gExtensionsViewController = {
       var name = aSelectedItem.getAttribute("name");
       var id = getIDFromResourceURI(aSelectedItem.id);
       var dependentItems = gExtensionManager.getDependentItemListForID(id, true, { });
-      var params = {
-        message2: getExtensionString("uninstallQueryMessage", [name]),
-        title: getExtensionString("uninstallTitle", [name]),
-        buttons: {
-          accept: { label: getExtensionString("uninstallButton"),
-                    focused: true },
-          cancel: { label: getExtensionString("cancelButton") }
-        }
-      }
-      if (dependentItems.length > 0)
-        params.message1 = getExtensionString("uninstallWarnDependMsg", [name]);
-      var names = [];
-      for (var i = 0; i < dependentItems.length; ++i)
-        names.push(dependentItems[i].name + " " + dependentItems[i].version);
-
-      window.openDialog("chrome://mozapps/content/extensions/list.xul", "", 
-                        "titlebar,modal,centerscreen", names, params);
-      if (params.result != "accept") 
+      var result = confirmOperation(name, "uninstallTitle", "uninstallQueryMessage",
+                                    "uninstallButton", "cancelButton",
+                                    "uninstallWarnDependMsg", dependentItems);
+      if (!result)
         return;
 
       if (aSelectedItem.type == nsIUpdateItem.TYPE_THEME) {
@@ -1876,6 +1894,39 @@ var gExtensionsViewController = {
       updateOptionalViews();
     },
 
+    cmd_cancelInstall: function (aSelectedItem)
+    {
+      var name = aSelectedItem.getAttribute("name");
+      var result = false;
+      // Confirm cancelling the operation
+      switch (aSelectedItem.opType)
+      {
+        case OP_NEEDS_INSTALL:
+          result = confirmOperation(name, "cancelInstallTitle", "cancelInstallQueryMessage",
+                                    "cancelInstallButton", "cancelCancelInstallButton",
+                                    null, []);
+          break;
+        case OP_NEEDS_UPGRADE:
+          result = confirmOperation(name, "cancelUpgradeTitle", "cancelUpgradeQueryMessage",
+                                    "cancelUpgradeButton", "cancelCancelUpgradeButton",
+                                    null, []);
+          break;
+      }
+      if (!result)
+        return;
+
+      gExtensionManager.cancelInstallItem(getIDFromResourceURI(aSelectedItem.id));
+      gExtensionsViewController.onCommandUpdate();
+      updateGlobalCommands();
+      gExtensionsView.selectedItem.focus();
+      updateOptionalViews();
+    },
+
+    cmd_cancelUpgrade: function (aSelectedItem)
+    {
+      this.cmd_cancelInstall(aSelectedItem);
+    },
+
     cmd_disable: function (aSelectedItem)
     {
       if (aSelectedItem.getAttribute("plugin") == "true") {
@@ -1888,24 +1939,10 @@ var gExtensionsViewController = {
 
       if (dependentItems.length > 0) {
         var name = aSelectedItem.getAttribute("name");
-        var message = getExtensionString("disableWarningDependMessage", [name]);
-        var params = {
-          message1: message,
-          message2: getExtensionString("disableQueryMessage", [name]),
-          title: getExtensionString("disableTitle", [name]),
-          buttons: {
-            accept: { label: getExtensionString("disableButton"),
-                      focused: true },
-            cancel: { label: getExtensionString("cancelButton") }
-          }
-        }
-        var names = [];
-        for (var i = 0; i < dependentItems.length; ++i)
-          names.push(dependentItems[i].name + " " + dependentItems[i].version);
-
-        window.openDialog("chrome://mozapps/content/extensions/list.xul", "", 
-                          "titlebar,modal,centerscreen", names, params);
-        if (params.result != "accept") 
+        var result = confirmOperation(name, "disableTitle", "disableQueryMessage",
+                                      "disableButton", "cancelButton",
+                                      "disableWarningDependMessage", dependentItems);
+        if (!result)
           return;
       }
       gExtensionManager.disableItem(id);
diff --git a/mozilla/toolkit/mozapps/extensions/content/extensions.xml b/mozilla/toolkit/mozapps/extensions/content/extensions.xml
index 8bf4b5d2aa2..2682e398069 100644
--- a/mozilla/toolkit/mozapps/extensions/content/extensions.xml
+++ b/mozilla/toolkit/mozapps/extensions/content/extensions.xml
@@ -274,6 +274,12 @@
             <xul:button class="uninstallShow cancelUninstallButton" label="&cancel.label;"
                         accesskey="&cancel.accesskey;" tooltiptext="&cmd.cancelUninstall.tooltip;"
                         command="cmd_cancelUninstall"/>
+            <xul:button class="installShow cancelInstallButton" label="&cancelInstall.label;"
+                        accesskey="&cancelInstall.accesskey;" tooltiptext="&cmd.cancelInstall.tooltip;"
+                        command="cmd_cancelInstall"/>
+            <xul:button class="upgradeShow cancelUpgradeButton" label="&cancelUpgrade.label;"
+                        accesskey="&cancelUpgrade.accesskey;" tooltiptext="&cmd.cancelUpgrade.tooltip;"
+                        command="cmd_cancelUpgrade"/>
           </xul:hbox>
         </xul:vbox>
       </xul:hbox>
diff --git a/mozilla/toolkit/mozapps/extensions/content/extensions.xul b/mozilla/toolkit/mozapps/extensions/content/extensions.xul
index eeaca243cdd..b8f290a62ea 100644
--- a/mozilla/toolkit/mozapps/extensions/content/extensions.xul
+++ b/mozilla/toolkit/mozapps/extensions/content/extensions.xul
@@ -93,6 +93,8 @@
     <command id="cmd_homepage"/>
     <command id="cmd_uninstall"/>
     <command id="cmd_cancelUninstall"/>
+    <command id="cmd_cancelInstall"/>
+    <command id="cmd_cancelUpgrade"/>
     <command id="cmd_checkUpdate"/>
     <command id="cmd_includeUpdate"/>
     <command id="cmd_installUpdate"/>
@@ -128,6 +130,10 @@
               label="&cmd.uninstall.label;" accesskey="&cmd.uninstall2.accesskey;"/>
     <menuitem id="menuitem_cancelUninstall" command="cmd_cancelUninstall"
               label="&cmd.cancelUninstall.label;" accesskey="&cmd.cancelUninstall.accesskey;"/>
+    <menuitem id="menuitem_cancelInstall" command="cmd_cancelInstall"
+              label="&cmd.cancelInstall.label;" accesskey="&cmd.cancelInstall.accesskey;"/>
+    <menuitem id="menuitem_cancelUpgrade" command="cmd_cancelUpgrade"
+              label="&cmd.cancelUpgrade.label;" accesskey="&cmd.cancelUpgrade.accesskey;"/>
     <menuitem id="menuitem_checkUpdate" command="cmd_checkUpdate"
               label="&cmd.checkUpdate.label;" accesskey="&cmd.checkUpdate.accesskey;"/>
     <menuitem id="menuitem_enable" command="cmd_enable"
diff --git a/mozilla/toolkit/mozapps/extensions/public/nsIExtensionManager.idl b/mozilla/toolkit/mozapps/extensions/public/nsIExtensionManager.idl
index 9e5a9c998c1..2d89b07ae0a 100644
--- a/mozilla/toolkit/mozapps/extensions/public/nsIExtensionManager.idl
+++ b/mozilla/toolkit/mozapps/extensions/public/nsIExtensionManager.idl
@@ -197,7 +197,7 @@ interface nsIInstallLocation : nsISupports
  * XXXben - Some of this stuff should go into a management-ey interface, 
  *          some into an app-startup-ey interface.
  */
-[scriptable, uuid(c2aef3c3-8ce1-4470-94e4-1167e5ca8928)]
+[scriptable, uuid(f5c34a77-3487-4b70-a65a-6727fa066324)]
 interface nsIExtensionManager : nsISupports
 {
   /**
@@ -406,6 +406,14 @@ interface nsIExtensionManager : nsISupports
    */
   void moveToIndexOf(in AString movingID, in AString destinationID);
 
+  /**
+   * Cancels a pending install or upgrade of an item. If the item does
+   * not have a pending install or upgrade then this will do nothing.
+   * @param   id
+   *          The ID of the item.
+   */
+  void cancelInstallItem(in AString id);
+
   /**
    * Cancels a pending uninstall of an item
    * @param   id
diff --git a/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in b/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
index c2dccf0aef6..da91c175364 100644
--- a/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
+++ b/mozilla/toolkit/mozapps/extensions/src/nsExtensionManager.js.in
@@ -4663,6 +4663,8 @@ ExtensionManager.prototype = {
         this._updateManifests(false);
       }
       else {
+        if (opType == OP_NEEDS_UPGRADE)
+          ds.setItemProperty(id, "newVersion", null);
         this._setOp(id, OP_NEEDS_UNINSTALL);
         var type = ds.getItemProperty(id, "type");
         var restartRequired = this.installRequiresRestart(id, type);
@@ -4681,6 +4683,53 @@ ExtensionManager.prototype = {
     this._notifyAction(id, EM_ITEM_UNINSTALLED);
   },
 
+  /* See nsIExtensionManager.idl */
+  cancelInstallItem: function(id) {
+    var ds = this.datasource;
+    var opType = ds.getItemProperty(id, "opType");
+    if (opType != OP_NEEDS_UPGRADE && opType != OP_NEEDS_INSTALL)
+      return;
+
+    ds.updateDownloadState(PREFIX_ITEM_URI + id, null);
+    var installLocation = this.getInstallLocation(id);
+    // Removes any staged xpis for this item.
+    var stageFile = installLocation.getStageFile(id);
+    if (stageFile)
+      installLocation.removeFile(stageFile);
+    // Addons with an opType of OP_NEEDS_INSTALL only have a staged xpi file
+    // and just need to be removed completely from the ds.
+    if (opType == OP_NEEDS_INSTALL) {
+      ds.removeItemMetadata(id);
+      ds.removeItemFromContainer(id);
+      ds.updateVisibleList(id, null, true);
+      StartupCache.clearEntry(installLocation, id);
+      this._updateManifests(false);
+      this._notifyAction(id, EM_ITEM_CANCEL);
+    }
+    else {
+      // Clear upgrade information and reset any request to enable/disable.
+      ds.setItemProperty(id, EM_R("newVersion"), null);
+      var appDisabled = ds.getItemProperty(id, "appDisabled");
+      var userDisabled = ds.getItemProperty(id, "userDisabled");
+      if (appDisabled == "true" || appDisabled == OP_NONE && userDisabled == OP_NONE) {
+        this._setOp(id, OP_NONE);
+        this._notifyAction(id, EM_ITEM_CANCEL);
+      }
+      else if (appDisabled == OP_NEEDS_DISABLE || userDisabled == OP_NEEDS_DISABLE) {
+        this._setOp(id, OP_NEEDS_DISABLE);
+        this._notifyAction(id, EM_ITEM_DISABLED);
+      }
+      else if (appDisabled == OP_NEEDS_ENABLE || userDisabled == OP_NEEDS_ENABLE) {
+        this._setOp(id, OP_NEEDS_ENABLE);
+        this._notifyAction(id, EM_ITEM_ENABLED);
+      }
+      else {
+        this._setOp(id, OP_NONE);
+        this._notifyAction(id, EM_ITEM_CANCEL);
+      }
+    }
+  },
+  
   /**
    * Cancels a pending uninstall of an item
    * @param   id
diff --git a/mozilla/toolkit/themes/pinstripe/mozapps/extensions/extensions.css b/mozilla/toolkit/themes/pinstripe/mozapps/extensions/extensions.css
index 50d76d4cf64..940f104af34 100644
--- a/mozilla/toolkit/themes/pinstripe/mozapps/extensions/extensions.css
+++ b/mozilla/toolkit/themes/pinstripe/mozapps/extensions/extensions.css
@@ -168,11 +168,15 @@ richlistitem[satisfiesDependencies="false"] .notifyBadge {
 
 .enableHide,
 .uninstallShow,
+.installShow,
+.upgradeShow,
 richlistitem[isDisabled="true"] .disableHide {
   display: none;
 }
 
 richlistitem[opType="needs-uninstall"] .uninstallShow,
+richlistitem[opType="needs-install"] .installShow,
+richlistitem[opType="needs-upgrade"] .upgradeShow,
 richlistitem[opType="needs-enable"] .enableShow,
 richlistitem[opType="needs-disable"] .disableShow,
 richlistitem[isDisabled="true"] .disableShow {
@@ -180,6 +184,8 @@ richlistitem[isDisabled="true"] .disableShow {
 }
 
 richlistitem[opType="needs-uninstall"] .uninstallHide,
+richlistitem[opType="needs-install"] .uninstallHide,
+richlistitem[opType="needs-upgrade"] .uninstallHide,
 richlistitem[opType="needs-enable"] .enableHide,
 richlistitem[opType="needs-disable"] .disableHide {
   display: none;
diff --git a/mozilla/toolkit/themes/winstripe/mozapps/extensions/extensions.css b/mozilla/toolkit/themes/winstripe/mozapps/extensions/extensions.css
index 2818655025c..df98c003e56 100644
--- a/mozilla/toolkit/themes/winstripe/mozapps/extensions/extensions.css
+++ b/mozilla/toolkit/themes/winstripe/mozapps/extensions/extensions.css
@@ -237,11 +237,15 @@ richlistitem[satisfiesDependencies="false"] .notifyBadge {
 
 .enableHide,
 .uninstallShow,
+.installShow,
+.upgradeShow,
 richlistitem[isDisabled="true"] .disableHide {
   display: none;
 }
 
 richlistitem[opType="needs-uninstall"] .uninstallShow,
+richlistitem[opType="needs-install"] .installShow,
+richlistitem[opType="needs-upgrade"] .upgradeShow,
 richlistitem[opType="needs-enable"] .enableShow,
 richlistitem[opType="needs-disable"] .disableShow,
 richlistitem[isDisabled="true"] .disableShow {
@@ -249,6 +253,8 @@ richlistitem[isDisabled="true"] .disableShow {
 }
 
 richlistitem[opType="needs-uninstall"] .uninstallHide,
+richlistitem[opType="needs-install"] .uninstallHide,
+richlistitem[opType="needs-upgrade"] .uninstallHide,
 richlistitem[opType="needs-enable"] .enableHide,
 richlistitem[opType="needs-disable"] .disableHide {
   display: none;