Remove about:buildconfig.  If used as-is, it would add unnecessary runtime dependencies.
diff -ru -x '*~' a/docshell/base/nsAboutRedirector.cpp b/docshell/base/nsAboutRedirector.cpp
--- a/docshell/base/nsAboutRedirector.cpp	2017-07-31 18:20:51.000000000 +0200
+++ b/docshell/base/nsAboutRedirector.cpp	2017-09-26 22:02:00.814151731 +0200
@@ -32,8 +32,6 @@
     {"about", "chrome://global/content/aboutAbout.xhtml", 0},
     {"addons", "chrome://mozapps/content/extensions/extensions.xul",
      nsIAboutModule::ALLOW_SCRIPT},
-    {"buildconfig", "chrome://global/content/buildconfig.html",
-     nsIAboutModule::URI_SAFE_FOR_UNTRUSTED_CONTENT},
     {"checkerboard", "chrome://global/content/aboutCheckerboard.xhtml",
      nsIAboutModule::URI_SAFE_FOR_UNTRUSTED_CONTENT |
          nsIAboutModule::ALLOW_SCRIPT},
diff -ru -x '*~' a/toolkit/content/jar.mn b/toolkit/content/jar.mn
--- a/toolkit/content/jar.mn	2017-07-31 18:20:52.000000000 +0200
+++ b/toolkit/content/jar.mn	2017-09-26 22:01:42.383350314 +0200
@@ -39,7 +39,6 @@
    content/global/plugins.css
    content/global/browser-child.js
    content/global/browser-content.js
-*   content/global/buildconfig.html
    content/global/buildconfig.css
    content/global/contentAreaUtils.js
    content/global/datepicker.xhtml
--- a/comm/mail/base/jar.mn
+++ b/comm/mail/base/jar.mn
@@ -117,9 +117,7 @@
 % override chrome://mozapps/content/profile/profileDowngrade.js chrome://messenger/content/profileDowngrade.js
 % override chrome://mozapps/content/profile/profileDowngrade.xul chrome://messenger/content/profileDowngrade.xul
 
-*   content/messenger/buildconfig.html              (content/buildconfig.html)
     content/messenger/buildconfig.css               (content/buildconfig.css)
-% override chrome://global/content/buildconfig.html chrome://messenger/content/buildconfig.html
 % override chrome://global/content/buildconfig.css chrome://messenger/content/buildconfig.css
 
 # L10n resources and overrides.