Closes issue #522.

common/modules/io.jsm

@@ -993,7 +993,7 @@ unlet s:cpo_save
             }
             if (!match || match.scheme === "resource" && match.path)
                 if (/^(\.{0,2}|~)\/|^file:/.test(context.filter)
-                    || util.OS.isWindows && /^[a-z]:/i.test(url)
+                    || util.OS.isWindows && /^[a-z]:/i.test(context.filter)
                     || util.getFile(context.filter)
                     || io.isJarURL(context.filter))
                     completion.file(context, full);