diff --git a/collects/browser/external.ss b/collects/browser/external.ss
index c567e2d132..7e18c9dc7c 100644
--- a/collects/browser/external.ss
+++ b/collects/browser/external.ss
@@ -20,7 +20,10 @@
 
   (fw:preferences:set-default
    'external-browser
-   (get-preference 'external-browser (lambda () #f))
+   (let ([ll-pref (get-preference 'external-browser (lambda () #f))])
+     (if (raw:browser-preference? ll-pref)
+         ll-pref
+         'firefox))
    raw:browser-preference?)
 
   (define http-proxy-preference 'plt:http-proxy)