update window.browser spec

Author: patrickkettner

specification/window.browser.bs

@@ -21,19 +21,19 @@ spec: html; urlPrefix: https://html.spec.whatwg.org/multipage/
 </pre>
 
 <section class="non-normative">
-  ## Introduction {#introduction}
+  ## Introduction
   <em>This section is non-normative.</em>
 
   Browser extensions are programs to extend the capabilities of web browsers.
   Although not standardized at first, web browsers have independently implemented a common interoperable set of extension APIs, called WebExtensions.
 
   Modern WebExtensions are an evolution of a system originally introduced in
-  Chrome version 3. In that system, any API that was added was put under the
+  Chromium. In that system, any API that was added was put under the
   <code>chrome</code> namespace. When WebExtensions were adopted outside of
   Chromium, other vendors used the more neutral <code>browser</code> namespace.
-  That <code>browser</code> is now considered to canonically correct namespace
+  That <code>browser</code> is now considered the canonically correct namespace
   for all WebExtension APIs.  Some interactions with WebExtensions (such as
-  external messaging from content scripts to background processes) necessitate
+  external messaging from websites to background processes) necessitate
   the exposure of this namespace to the web.
 
   Given that, this document defines <code>window.browser</code> as reserved for
@@ -65,15 +65,12 @@ spec: html; urlPrefix: https://html.spec.whatwg.org/multipage/
       Worker API
     </h3>
 
-    When {{browser}} is defined on {{window}}, it SHOULD also be implemented on {{ServiceWorkerGlobalScope}} and {{DedicatedWorkerGlobalScope}}.
-    It MUST be used exclusivly for WebExtension purposes, however the contents of each instance of {{browser}} is UA defined.
+    When {{browser}} is defined on {{window}}, it SHOULD also be exposed on {{ServiceWorkerGlobalScope}}
+    of origins associated with WebExtensions.
+    It MUST be used exclusively for WebExtension purposes, however the contents of each instance of {{browser}} is UA defined.
   </section>
 
 <pre class="idl">
-  partial interface DedicatedWorkerGlobalScope {
-    attribute object browser;
-  };
-
   partial interface ServiceWorkerGlobalScope {
     attribute object browser;
   };