MB 34: Hide unsafe and unwanted preferences UI

about:preferences allow to override some of our defaults, that could
be fingeprintable or have some other unwanted consequences.

browser/components/preferences/privacy.inc.xhtml

@@ -1065,7 +1065,7 @@
 #include ../securitylevel/content/securityLevelPreferences.inc.xhtml
 
 <!-- addons, forgery (phishing) UI Security -->
-<groupbox id="browsingProtectionGroup" data-category="panePrivacy" hidden="true">
+<groupbox id="browsingProtectionGroup" data-category="panePrivacy" hidden="true" data-hidden-from-search="true">
   <label><html:h2 data-l10n-id="security-browsing-protection"/></label>
   <hbox align = "center">
     <checkbox id="enableSafeBrowsing"

browser/components/preferences/search.inc.xhtml

@@ -37,7 +37,7 @@
       </vbox>
     </groupbox>
 
-    <groupbox id="searchSuggestionsGroup" data-category="paneSearch" hidden="true">
+    <groupbox id="searchSuggestionsGroup" data-category="paneSearch" hidden="true" data-hidden-from-search="true">
       <label><html:h2 data-l10n-id="search-suggestions-header" /></label>
       <description id="searchSuggestionsDesc"
                    class="description-deemphasized"
@@ -202,7 +202,7 @@
                 "
                 />
       </hbox>
-      <hbox id="addEnginesBox" pack="start">
+      <hbox id="addEnginesBox" pack="start" hidden="true">
         <label id="addEngines" data-l10n-id="search-find-more-link" is="text-link"></label>
       </hbox>
     </groupbox>