fixup! Bug 40925: Implemented the Security Level component

Bug 42583: Use moz-support-link for the security level "Learn more"
links. These take you to the tor project web link in base browser.

browser/components/securitylevel/content/securityLevel.js

@@ -157,6 +157,9 @@ var SecurityLevelPanel = {
   _populated: false,
 
   _populateXUL() {
+    // TODO: Used for #securityLevel-learnMore. Remove with esr 128.
+    window.ensureCustomElements("moz-support-link");
+
     this._elements = {
       panel: document.getElementById("securityLevel-panel"),
       background: document.getElementById("securityLevel-background"),
@@ -171,9 +174,7 @@ var SecurityLevelPanel = {
 
     const learnMoreEl = document.getElementById("securityLevel-learnMore");
     learnMoreEl.addEventListener("click", event => {
-      window.openTrustedLinkIn(learnMoreEl.href, "tab");
       this.hide();
-      event.preventDefault();
     });
 
     this._elements.restoreDefaultsButton.addEventListener("command", () => {

browser/components/securitylevel/content/securityLevelPanel.inc.xhtml

@@ -23,9 +23,10 @@
     </html:p>
     <html:p id="securityLevel-summary"></html:p>
     <html:a
+      is="moz-support-link"
       id="securityLevel-learnMore"
+      tor-manual-page="security-settings"
       data-l10n-id="security-level-panel-learn-more-link"
-      href="https://mullvad.net/en/browser/hard-facts#security-levels"
     ></html:a>
   </vbox>
   <hbox class="panel-footer">

browser/components/securitylevel/content/securityLevelPreferences.inc.xhtml

@@ -12,13 +12,11 @@
         class="tail-with-learn-more"
         data-l10n-id="security-level-preferences-overview"
       ></html:span>
-      <label
-        id="securityLevel-learnMore"
-        class="learnMore text-link"
-        is="text-link"
+      <html:a
+        is="moz-support-link"
+        tor-manual-page="security-settings"
         data-l10n-id="security-level-preferences-learn-more-link"
-        href="https://mullvad.net/en/browser/hard-facts#security-levels"
-      />
+      ></html:a>
     </description>
     <hbox
       id="securityLevel-customNotification"