Bug 1838939 - Part 3: Use headings in various about pages r=desktop-theme-reviewers,dao

Differential Revision: https://phabricator.services.mozilla.com/D186032

browser/components/enterprisepolicies/content/aboutPolicies.html

@@ -42,11 +42,11 @@
     </div>
     <div class="main-content">
       <div class="header">
-        <div
+        <h1
           id="sectionTitle"
           class="header-name"
           data-l10n-id="active-policies-tab"
-        ></div>
+        ></h1>
       </div>
 
       <div id="active" class="tab active">

toolkit/content/aboutNetworking.html

@@ -62,11 +62,11 @@
     </div>
     <div class="main-content">
       <div class="header">
-        <div
+        <h1
           id="sectionTitle"
           class="header-name"
           data-l10n-id="about-networking-http"
-        ></div>
+        ></h1>
         <div id="refreshDiv">
           <button
             id="refreshButton"

toolkit/content/aboutTelemetry.xhtml

@@ -205,7 +205,7 @@
       </div>
 
       <div class="header">
-        <div
+        <h1
           id="sectionTitle"
           class="header-name"
           data-l10n-id="about-telemetry-page-title"