One word: Internet Explorer 6. This includes a rewrite of $paths->parseAdminTree() that encodes to JSON instead of manually generating JS, so good-bye to stupid parser problems I hope.
/*
* Auto-completing page/username fields
* NOTE: A more efficient version of the username field is used for Mozilla browsers. The updated code is in autofill.js.
*/
//
// **** 1.1.5: DEPRECATED ****
// Replaced with jQuery-based mechanism.
//