diff --git a/toolkit/content/widgets/autocomplete.xml b/toolkit/content/widgets/autocomplete.xml
index 5532a44810a..1647379a3f0 100644
--- a/toolkit/content/widgets/autocomplete.xml
+++ b/toolkit/content/widgets/autocomplete.xml
@@ -157,7 +157,7 @@
                 onget="return parseInt(this.getAttribute('timeout')) || 50;"/>
 
       <property name="searchParam"
-                onget="return this.getAttribute('autocompletesearchparam');"
+                onget="return this.getAttribute('autocompletesearchparam') || '';"
                 onset="this.setAttribute('autocompletesearchparam', val); return val;"/>
 
       <property name="searchCount" readonly="true"