Updated the autocomplete to have a bit more intelligence.

 -- Filter out search term results to only include things that start with the search term.
 -- Highlight the matching term from the item
 -- Ran code through jslint and fixed numerous mistakes.
Modified the browser backend so it does not throw an assertion error for invalid paths anymore. As this serves no purpose for the pathbrowser except an ugly ajax error in the console.

data/js/browser.js

@@ -8,19 +8,19 @@
         }
     };
 
-    var fileBrowserDialog  = null;
-    var currentBrowserPath = null;
-    var currentRequest     = null;
+    var fileBrowserDialog, currentBrowserPath, currentRequest = null;
 
     function browse(path, endpoint) {
 
-        if(currentBrowserPath == path)
+        if (currentBrowserPath === path) {
             return;
+        }
 
         currentBrowserPath = path;
 
-        if(currentRequest)
+        if (currentRequest) {
             currentRequest.abort();
+        }
 
         fileBrowserDialog.dialog('option', 'dialogClass', 'browserDialog busy');
 
@@ -28,7 +28,8 @@
             fileBrowserDialog.empty();
             var first_val = data[0];
             var i = 0;
-            data = jQuery.grep(data, function(value) {
+            var list, link = null;
+            data = $.grep(data, function (value) {
                 return i++ != 0;
             });
             $('<h1>').text(first_val.current_path).appendTo(fileBrowserDialog);
@@ -37,8 +38,8 @@
                 link = $("<a href='javascript:void(0)' />").click(function () { browse(entry.path, endpoint); }).text(entry.name);
                 $('<span class="ui-icon ui-icon-folder-collapsed"></span>').prependTo(link);
                 link.hover(
-                    function(){jQuery("span", this).addClass("ui-icon-folder-open");    },
-                    function(){jQuery("span", this).removeClass("ui-icon-folder-open"); }
+                    function () {$("span", this).addClass("ui-icon-folder-open");    },
+                    function () {$("span", this).removeClass("ui-icon-folder-open"); }
                 );
                 link.appendTo(list);
             });
@@ -68,30 +69,25 @@
         }
 
         // add the OK/Close buttons to the dialog
-        fileBrowserDialog.dialog('option', 'buttons',
-        {
+        fileBrowserDialog.dialog('option', 'buttons', {
             "Ok": function () {
-                
                 // store the browsed path to the associated text field
                 //options.field.val(currentBrowserPath);
                 //alert(currentBrowserPath);
                 callback(currentBrowserPath, options);
-                
                 fileBrowserDialog.dialog("close");
             },
-
             "Cancel": function () {
                 fileBrowserDialog.dialog("close");
             }
-            
         });
 
         // set up the browser and launch the dialog
-        if (options.initialDir)
+        var initialDir = '';
+        if (options.initialDir) {
             initialDir = options.initialDir;
-        else
-            initialDir = '';
-        browse(initialDir, options.url)
+        }
+        browse(initialDir, options.url);
         fileBrowserDialog.dialog('open');
 
         return false;
@@ -99,43 +95,71 @@
 
     $.fn.fileBrowser = function (options) {
         options = $.extend({}, $.Browser.defaults, options);
-        
         // text field used for the result
         options.field = $(this);
 
         if (options.field.autocomplete && options.autocompleteURL) {
+            var query = '';
             options.field.autocomplete({
-                source: options.autocompleteURL,
+                source: function (request, response) {
+                    //keep track of user submitted search term
+                    query = $.ui.autocomplete.escapeRegex(request.term);
+                    $.ajax({
+                        url: options.autocompleteURL,
+                        data: request,
+                        dataType: "json",
+                        success: function (data, item) {
+                            //implement a startsWith filter for the results
+                            var matcher = new RegExp("^" + query, "i");
+                            var a = $.grep(data, function (item, index) {
+                                return matcher.test(item);
+                            });
+                            response(a);
+                        }
+                    });
+                },
                 open: function (event, ui) {
                     $(".ui-autocomplete li.ui-menu-item a").removeClass("ui-corner-all");
                     $(".ui-autocomplete li.ui-menu-item:odd a").addClass("ui-menu-item-alternate");
                 }
+            })
+                .data("autocomplete")._renderItem = function (ul, item) {
+                    //highlight the matched search term from the item -- note that this is global and will match anywhere
+                    var result_item = item.label;
+                    var x = new RegExp("(?![^&;]+;)(?!<[^<>]*)(" + query + ")(?![^<>]*>)(?![^&;]+;)", "gi");
+                    result_item = result_item.replace(x, function (FullMatch, n) {
+                        return '<b>' + FullMatch + '</b>';
                     });
+                    return $("<li></li>")
+                        .data("item.autocomplete", item)
+                        .append("<a class='nowrap'>" + result_item + "</a>")
+                        .appendTo(ul);
+                };
         }
 
+        var initialDir, path, callback = null;
         // if the text field is empty and we're given a key then populate it with the last browsed value from a cookie
-        if(options.key && options.field.val().length == 0 && (path = $.cookie('fileBrowser-' + options.key)))
+        if (options.key && options.field.val().length === 0 && (path = $.cookie('fileBrowser-' + options.key))) {
             options.field.val(path);
+        }
 
         callback = function (path, options) {
             // store the browsed path to the associated text field
             options.field.val(path);
 
             // use a cookie to remember for next time
-            if(options.key)
+            if (options.key) {
                 $.cookie('fileBrowser-' + options.key, path);
-        
             }
+        };
 
         initialDir = options.field.val() || (options.key && $.cookie('fileBrowser-' + options.key)) || '';
 
-        options = $.extend(options, {initialDir: initialDir})
+        options = $.extend(options, {initialDir: initialDir});
 
         // append the browse button and give it a click behavior
         return options.field.addClass('fileBrowserField').after($('<input type="button" value="Browse&hellip;" class="fileBrowser" />').click(function () {
-            
             $(this).nFileBrowser(callback, options);
-            
             return false;
         }));
     };

sickbeard/browser.py

@@ -52,7 +52,6 @@ def foldersAtPath(path, includeParent = False):
         Give the empty string as the path to list the contents of the root path
         under Unix this means "/", on Windows this will be a list of drive letters)
     """
-    assert os.path.isabs(path) or path == ""
 
     # walk up the tree until we find a valid path
     while path and not os.path.isdir(path):