rosa-build/app/views/projects/base/_branch_select.html.haml

.lineForm.fork
  = select_tag :branch, branch_selector_options(project), :id => 'branch_selector', :class => 'sel80'
  %form{:action => '', :method => :get, :id => 'branch_changer', :'data-action' => "#{controller_name}"}
.fork
  %p #{t('layout.projects.current_branch')}:
.both

:javascript
  $(document).ready(function() {
    $('select#branch_selector').live('change', function(e) {
      $form = $('form#branch_changer');
      $form.attr('action', $(this).val());
      $form.submit();
    });
  });