diff --git a/toolkit/mozapps/downloads/content/helperApps.js b/toolkit/mozapps/downloads/content/helperApps.js
index 3f9fb31ce5bd..e5884a1bc1f7 100755
--- a/toolkit/mozapps/downloads/content/helperApps.js
+++ b/toolkit/mozapps/downloads/content/helperApps.js
@@ -597,7 +597,13 @@ HandlerOverride.prototype = {
   
   set appDisplayName(aDisplayName)
   {
-    this.changeMIMEStuff(APP_URI(this.mimeType), "prettyName", aDisplayName);
+    if (aDisplayName)
+      this.changeMIMEStuff(APP_URI(this.mimeType), "prettyName", aDisplayName);
+    else {
+      var currentValue = this.getLiteralForContentType(APP_URI(this.mimeType), "prettyName");
+      this.unassertMIMEStuff(APP_URI(this.mimeType), "prettyName", currentValue);
+    }
+
     return aDisplayName;
   },
   
@@ -608,7 +614,13 @@ HandlerOverride.prototype = {
   
   set appPath(aAppPath)
   {
-    this.changeMIMEStuff(APP_URI(this.mimeType), "path", aAppPath);
+    if (aAppPath)
+      this.changeMIMEStuff(APP_URI(this.mimeType), "path", aAppPath);
+    else {
+      var currentValue = this.getLiteralForContentType(APP_URI(this.mimeType), "path");
+      this.unassertMIMEStuff(APP_URI(this.mimeType), "path", currentValue);
+    }
+
     return aAppPath;
   },