Bug 1465583 - Disable early blank first paint on all channels except Nightly. r=Felipe

MozReview-Commit-ID: 5udkj1hjw7H

--HG--
extra : rebase_source : a46a0e6bc548c8e1eb96445e35cbf9eac9b80f85

browser/app/profile/firefox.js

@@ -250,9 +250,8 @@ pref("browser.startup.homepage",            "chrome://branding/locale/browsercon
 pref("browser.startup.firstrunSkipsHomepage", true);
 
 // Show an about:blank window as early as possible for quick startup feedback.
-// Held to nightly and early beta on Linux due to bug 1450626.
 // Disabled on Mac because the bouncing dock icon already provides feedback.
-#if defined(XP_WIN) || defined(MOZ_WIDGET_GTK) && defined(EARLY_BETA_OR_EARLIER)
+#if !defined(XP_MACOSX) && defined(NIGHTLY_BUILD)
 pref("browser.startup.blankWindow", true);
 #else
 pref("browser.startup.blankWindow", false);