Focus the notification popup if it's already open

Any action in the background that would have opened the notification
window will now focus the window instead if it was already open.
Previously it would leave the window unfocused. This was particularly
inconvenient when taking multiple actions in quick succession that all
require confirmations (e.g. triggering multiple transactions).

app/scripts/background.js

@@ -458,7 +458,7 @@ function setupController (initState, initLangCode) {
 async function triggerUi () {
   const tabs = await platform.getActiveTabs()
   const currentlyActiveMetamaskTab = Boolean(tabs.find((tab) => openMetamaskTabsIDs[tab.id]))
-  if (!popupIsOpen && !currentlyActiveMetamaskTab && !notificationIsOpen) {
+  if (!popupIsOpen && !currentlyActiveMetamaskTab) {
     await notificationManager.showPopup()
   }
 }