Firefox select menu truncation - Rails or JQuery issue?

I have a Rails 4.1 app which has a "Region" select menu generated from a partial and which displays fine. Based on which option is selected from this menu I have a JQuery script which takes data from a "locations" var/object and constructs a secondary "Location" select menu. Everything works fine in Chrome and Safari but in the latest Firefox/Mac the secondary menu is limited to the first 20 items. WAT?? Could this be a Rails issue or an obscure Firefox bug?

gvim

ERB:
       <tr>
         <td align="right">Birth Place</td><td><%= render 'birth_region', {person: 1} %></td>
       </tr>
       <tr>
         <td align="right">&nbsp;</td><td><div id="sel1"></div></td>
       </tr>

ERB PARTIAL:
<% regions = %w(Africa America Antarctica Arctic Asia Atlantic Australia Brazil Canada Chile Europe Indian Mexico Pacific US Other) %>
             <select id="region<%= person %>" name="region<%= person %>">
               <option value="" selected="selected">-- Select Region --</option>
               <% regions.each do |region| %>
               <option value="<%= region %>"><%= region %></option>
               <% end %>
             </select>

JQUERY:

var locations = {
"Africa":{"Africa/Abidjan":"Abidjan","Africa/Accra":"Accra","Africa/Addis_Ababa":"Addis Ababa","Africa/Algiers":"Algiers","Africa/Asmara":"Asmara","Africa/Asmera":"Asmera","Africa/Bamako":"Bamako", ........ },

........

};

$(function() {
     $('select#region1').change(function() {
       var selection = $(this).val();
       var menu = '<select name="zone1"><option selected="selected" value="">-- Nearest Location --</option>';
       var reg = locations[selection];
       for (var key in reg) {
         menu += '<option value="' + key + '">' + reg[key] + '</option>';
       }
       menu += '</select>';
       $('div#sel1').html(menu);
     });
});