--- a/dom/apps/src/AppsUtils.jsm
+++ b/dom/apps/src/AppsUtils.jsm
@@ -464,17 +464,17 @@ ManifestHelper.prototype = {
       return this._origin.resolve(entryPoints[aStartPoint].launch_path || "");
     }
 
     return null;
   },
 
   resolveFromOrigin: function(aURI) {
     // This should be enforced higher up, but check it here just in case.
-    if (!isAbsoluteURI(aURI)) {
+    if (isAbsoluteURI(aURI)) {
       throw new Error("Webapps.jsm: non-relative URI passed to resolveFromOrigin");
     }
     return this._origin.resolve(aURI);
   },
 
   fullAppcachePath: function() {
     let appcachePath = this._localeProp("appcache_path");
     return this._origin.resolve(appcachePath ? appcachePath : "");