Issue #2886904 by jhodgdon, andrewmacpherson, volkerk, Eric Heydrich, Vidushi...

Issue #2886904 by jhodgdon, andrewmacpherson, volkerk, Eric Heydrich, Vidushi Mehta, Utkarsh_Mishra, jenlampton, hosef, anavarre, adriancid, xjm, alexpott, mgerbault, tracipotocnik, BSpeel, yoroy, lauriii: display: block for details/summary hides drop arrows in Firefox (normalize.css update)

core/core.libraries.yml

@@ -890,6 +890,7 @@ normalize:
   css:
     base:
       assets/vendor/normalize-css/normalize.css: { weight: -20 }
+      misc/normalize-fixes.css: { weight: -19 }
 
 picturefill:
   remote: https://github.com/scottjehl/picturefill

core/misc/normalize-fixes.css

+/**
+ * @file
+ * Fixes for core/assets/vendor/normalize-css/normalize.css since version 3.
+ */
+
+/**
+ * Fix problem with details/summary lines missing the drop arrows.
+ */
+@-moz-document url-prefix() {
+  summary {
+    display: list-item;
+  }
+}