Remove about:buildconfig.  If used as-is, it would add unnecessary runtime dependencies.
diff -ur firefox-65.0-orig/docshell/base/nsAboutRedirector.cpp firefox-65.0/docshell/base/nsAboutRedirector.cpp
--- firefox-76.0.orig/docshell/base/nsAboutRedirector.cpp       2020-05-03 19:01:29.926544735 +0200
+++ firefox-76.0/docshell/base/nsAboutRedirector.cpp    2020-05-03 19:12:00.845035570 +0200
@@ -62,8 +62,6 @@
     {"about", "chrome://global/content/aboutAbout.html", 0},
     {"addons", "chrome://mozapps/content/extensions/extensions.xhtml",
      nsIAboutModule::ALLOW_SCRIPT},
-    {"buildconfig", "chrome://global/content/buildconfig.html",
-     nsIAboutModule::URI_SAFE_FOR_UNTRUSTED_CONTENT},
     {"checkerboard", "chrome://global/content/aboutCheckerboard.html",
      nsIAboutModule::URI_SAFE_FOR_UNTRUSTED_CONTENT |
          nsIAboutModule::ALLOW_SCRIPT},
diff -ur firefox-65.0-orig/toolkit/content/jar.mn firefox-65.0/toolkit/content/jar.mn
--- firefox-65.0-orig/toolkit/content/jar.mn    2019-01-23 00:48:35.033372506 +0100
+++ firefox-65.0/toolkit/content/jar.mn 2019-01-23 00:50:45.126565924 +0100
@@ -36,7 +36,6 @@
    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