Bug 1000592 - Enable CSS Grid by default in non-release channels. r=dholbert

modules/libpref/init/all.js

@@ -2357,7 +2357,11 @@ pref("layout.css.variables.enabled", true);
 pref("layout.css.overflow-clip-box.enabled", false);
 
 // Is support for CSS grid enabled?
+#ifdef RELEASE_BUILD
 pref("layout.css.grid.enabled", false);
+#else
+pref("layout.css.grid.enabled", true);
+#endif
 
 // Is support for CSS contain enabled?
 pref("layout.css.contain.enabled", false);