diff -p -up mozilla-release/browser/app/profile/firefox.js.defaultbrowser mozilla-release/browser/app/profile/firefox.js
--- mozilla-release/browser/app/profile/firefox.js.defaultbrowser	2012-04-23 10:16:01.000000000 +0200
+++ mozilla-release/browser/app/profile/firefox.js	2012-04-23 10:18:28.965732670 +0200
@@ -250,7 +250,7 @@ pref("general.autoScroll", true);
 #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);
 
 // 0 = blank, 1 = home (browser.startup.homepage), 2 = last visited page, 3 = resume previous browser session
 // The behavior of option 3 is detailed at: http://wiki.mozilla.org/Session_Restore