Bug 1526517 - disable low-end-machine adjustment for beta and limit to nightly builds, r=mconley

Differential Revision: https://phabricator.services.mozilla.com/D19437

--HG--
extra : moz-landing-system : lando

modules/libpref/init/all.js

@@ -968,7 +968,7 @@ pref("gfx.webrender.dl.dump-parent", false);
 pref("gfx.webrender.dl.dump-content", false);
 pref("gfx.webrender.picture-caching", true);
 
-#ifdef EARLY_BETA_OR_EARLIER
+#ifdef NIGHTLY_BUILD
 pref("performance.adjust_to_machine", true);
 #else
 pref("performance.adjust_to_machine", false);