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	2013-06-25 19:43:40.900524326 +0400
+++ mozilla-release/browser/app/profile/firefox.js	2013-06-25 19:51:11.129550256 +0400
@@ -227,7 +227,7 @@
 pref("general.useragent.complexOverride.moodle", false); // bug 797703
 
 // 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