diff -urN mozilla-release.orig/browser/app/profile/firefox.js mozilla-release/browser/app/profile/firefox.js
--- mozilla-release.orig/browser/app/profile/firefox.js	2013-11-05 14:15:35.995958941 +0400
+++ mozilla-release/browser/app/profile/firefox.js	2013-11-05 14:17:28.267079493 +0400
@@ -231,7 +231,7 @@
 #endif
 
 // At startup, check if we're the default browser and prompt user if not.
-pref("browser.shell.checkDefaultBrowser", true);
+pref("browser.shell.checkDefaultBrowser", false);
 pref("browser.shell.shortcutFavicons",true);
 
 // 0 = blank, 1 = home (browser.startup.homepage), 2 = last visited page, 3 = resume previous browser session