--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -778,16 +778,17 @@ pref("gecko.handlerService.schemes.ircs.
 
 // By default, we don't want protocol/content handlers to be registered from a different host, see bug 402287
 pref("gecko.handlerService.allowRegisterFromDifferentHost", false);
 
 #ifdef MOZ_SAFE_BROWSING
 pref("browser.safebrowsing.downloads.enabled", true);
 pref("browser.safebrowsing.downloads.remote.enabled", true);
 pref("browser.safebrowsing.downloads.remote.block_potentially_unwanted", true);
+pref("browser.safebrowsing.downloads.remote.block_uncommon", true);
 
 #ifdef MOZILLA_OFFICIAL
 // Normally the "client ID" sent in updates is appinfo.name, but for
 // official Firefox releases from Mozilla we use a special identifier.
 pref("browser.safebrowsing.id", "navclient-auto-ffox");
 #endif
 
 // Name of the about: page contributed by safebrowsing to handle display of error