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docs/static/css/extra.css

+article {
+    padding-bottom: 50px;
+}
+
 figure img {
     border-radius: 7px;
     filter: drop-shadow(3px 3px 5px #ccc);

docs/subscribe/phone.md

@@ -11,9 +11,35 @@ the F-Droid flavor does not use Firebase.
 <a href="https://play.google.com/store/apps/details?id=io.heckel.ntfy"><img src="../../static/img/badge-googleplay.png"></a>
 <a href="https://f-droid.org/en/packages/io.heckel.ntfy/"><img src="../../static/img/badge-fdroid.png"></a>
 
-### Firebase + Instant delivery
+### Instant delivery
+Instant delivery is allows you to receive messages on your phone instantly, **even when your phone is in doze mode**, i.e. 
+when the screen turns off, and you leave it on the desk for a while. This is achieved with a foreground service, which 
+you'll see as a permanent notification that looks like this:
 
+<figure markdown>
+  ![foreground service](../static/img/foreground-service.png){ width=500 }
+  <figcaption>Instant delivery foreground notification</figcaption>
+</figure>
 
+Android does not allow you to dismiss this notification, unless you turn off the notification channel in the settings.
+To do so, long-press on the foreground notification (screenshot above) and navigate to the settings. Then toggle the 
+"Subscription Service" off:
+
+<figure markdown>
+  ![foreground service](../static/img/notification-settings.png){ width=500 }
+  <figcaption>Turning off the persistent instant delivery notification</figcaption>
+</figure>
+
+### Limitations without instant delivery
+Without instant delivery, **messages may arrive with a significant delay** (sometimes many minutes, or even hours later). If you've ever picked up your phone and 
+suddenly had 10 messages that were sent long before you know what I'm talking about.
+
+The reason for this is [Firebase Cloud Messaging (FCM)](https://firebase.google.com/docs/cloud-messaging). FCM is the 
+*only* Google approved way to send push messages to Android devices, and it's what pretty much all apps use to deliver push 
+notifications. Firebase is overall pretty bad at delivering messages in time, but on Android, most apps are stuck with it.
+
+The ntfy Android app uses Firebase only for the main host `ntfy.sh`, and only in the Google Play flavor of the app.
+It won't use Firebase for any self-hosted servers, and not at all in the the F-Droid flavor.
 
 ## iPhone/iOS
 I almost feel devious for putting the *Download on the App Store* button on this page. Currently, there is no iOS app