Add docs detailing web notification support

docs/known-issues.md

@@ -26,3 +26,13 @@ Be sure that in your selfhosted server:
 
 * Set `upstream-base-url: "https://ntfy.sh"` (**not your own hostname!**)
 * Ensure that the URL you set in `base-url` **matches exactly** what you set the Default Server in iOS to 
+
+## Firefox on Android not automatically subscribing to web push
+ntfy defaults to web-push based subscriptions when installed as a [progressive web app](./subscribe/pwa.md). Firefox
+Android has an [open bug](https://bugzilla.mozilla.org/show_bug.cgi?id=1796434) where it reports the PWA mode incorrectly.
+This causes ntfy to not automatically subscribe to web push, and requires you to go to the ntfy Settings page to enable
+it manually.
+
+## Safari does not play sounds for web push notifications
+Safari does not support playing sounds for web push notifications, and treats them all as silent. This will be fixed with
+iOS 17 / Safari 17, which will be released later in 2023.

docs/subscribe/web.md

@@ -23,6 +23,25 @@ If topic reservations are enabled, you can claim ownership over topics and defin
     <a href="../../static/img/web-reserve-topic-dialog.png"><img src="../../static/img/web-reserve-topic-dialog.png"/></a>
 </div>
 
+## Notification features and browser support
+
+- Emoji tags are supported in all browsers
+
+- [Click](../publish.md#click-action) actions are supported in all browsers
+
+- Only Chrome, Edge, and Opera support displaying view and http [actions](../publish.md#action-buttons) in notifications.
+
+  Their presentation is platform specific.
+  
+  Note that HTTP actions are performed using fetch and thus are limited to the [CORS](https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS)
+  rules, which means that any URL you include needs to respond to a [preflight request](https://developer.mozilla.org/en-US/docs/Glossary/Preflight_request)
+  with headers allowing the origin of the ntfy web app (`Access-Control-Allow-Origin: https://ntfy.sh`) or `*`.
+
+- Only Chrome, Edge, and Opera support displaying [images](../publish.md#attachments) in notifications.
+
+Look at the [Notifications API](https://developer.mozilla.org/en-US/docs/Web/API/Notifications_API#browser_compatibility)
+for more info.
+
 ## Background notifications
 While subscribing, you have the option to enable background notifications on supported browsers (see "Settings" tab).
 
@@ -50,6 +69,7 @@ by opening the app again, and will get a warning notification before they are pa
 | Opera   | Desktop  | ✅               | ❌                   |                                                         |
 | Safari  | Desktop  | ✅               | ✅                   | requires Safari 16.1, macOS 13 Ventura                  |
 | Chrome  | Android  | ✅               | ✅                   |                                                         |
+| Firefox | Android  | ✅               | ✅                   |                                                         |
 | Safari  | iOS      | ⚠️              | ⚠️                  | requires iOS 16.4, only when app is added to homescreen |
 
 (Browsers below 1% usage not shown, look at the [Push API](https://caniuse.com/push-api) for more info)