--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -1078,17 +1078,17 @@ pref("security.sandbox.gpu.level", 0);
 // 2 -> "preliminary content sandboxing enabled with profile protection:
 //       write access to home directory is prevented, read and write access
 //       to ~/Library and profile directories are prevented (excluding
 //       $PROFILE/{extensions,weave})"
 // This setting is read when the content process is started. On Mac the content
 // process is killed when all windows are closed, so a change will take effect
 // when the 1st window is opened.
 #if defined(NIGHTLY_BUILD)
-pref("security.sandbox.content.level", 2);
+pref("security.sandbox.content.level", 3);
 #else
 pref("security.sandbox.content.level", 1);
 #endif
 #endif
 
 #if defined(XP_LINUX) && defined(MOZ_SANDBOX) && defined(MOZ_CONTENT_SANDBOX)
 // This pref is introduced as part of bug 742434, the naming is inspired from
 // its Windows/Mac counterpart, but on Linux it's an integer which means: