After adding to an array in one method, the array appears empty in another

Question

The following is outputting an empty unordered list. Why? Many thanks, Steven.

module BrowserHelper

  def project_browser_helper
    if @project || @controller.controller_name == "projects"
      content_tag(:div, content_tag(:ul, build_browser), :class => "browser")
    end
  end

  def build_browser
    @browser = []
    # a whole bunch of if/elsif/else statements
    # that call methods that add elements to @browser
    # including the following method
    # which is definitely called in this case
    show_an_all_projects_list_item
    @browser.map { |list_item| content_tag(:li, list_item['body'], :id => list_item['id'], :class => list_item['class']) }
  end

  def show_an_all_projects_list_item
    list_item = Hash.new
    list_item['body'] = ["All projects (", Project.find(:all).size.to_s, ")"].join
    list_item['class'] = "all_projects"
    list_item['id'] = "XXX"
    @browser << list_item
  end

end

I don't think it's a scope issue, as I get the same problem when I use $browser instead of @browser.

However, I am sure it relates to the value of @browser not persisting between methods, as when I copy the content of def show_an_all_projects_list_item into def build_browser just above the @browser.map statement, it works fine -- I get the expected <li> in my <ul>.