User session never ends in Mozilla

Hello,

I am using ASP.NET and the web.config file below.
My problem is that if I open a page protected with this authentication with Mozilla, the session never expires, so the user is always logged in. With IE this problem does not exist.

-->
    <authentication mode="Forms" />

      <!--  AUTHORIZATION
          This section sets the authorization policies of the application. You can allow or deny access
          to application resources by user or role. Wildcards: "*" mean everyone, "?" means anonymous
          (unauthenticated) users.
    -->

    <authorization>
        <deny users="?" /> <!-- Allow all users -->
            <!--  <allow     users="[comma separated list of users]"
                             roles="[comma separated list of roles]"/>
                  <deny      users="[comma separated list of users]"
                             roles="[comma separated list of roles]"/>
            -->
    </authorization>

    <!--  APPLICATION-LEVEL TRACE LOGGING
          Application-level tracing enables trace log output for every page within an application.
          Set trace enabled="true" to enable application trace logging.  If pageOutput="true", the
          trace information will be displayed at the bottom of each page.  Otherwise, you can view the
          application trace log by browsing the "trace.axd" page from your web application
          root.
    -->
    <trace
        enabled="false"
        requestLimit="10"
        pageOutput="false"
        traceMode="SortByTime"
            localOnly="true"
    />

    <!--  SESSION STATE SETTINGS
          By default ASP.NET uses cookies to identify which requests belong to a particular session.
          If cookies are not available, a session can be tracked by adding a session identifier to the URL.
          To disable cookies, set sessionState cookieless="true".
    -->
    <sessionState
            mode="InProc"
            stateConnectionString="tcpip=127.0.0.1:42424"
            sqlConnectionString="data source=127.0.0.1;Trusted_Connection=yes"
            cookieless="false"
            timeout="1"
    />

And the following code in ASP.NET when user authenticated:

FormsAuthentication.RedirectFromLoginPage(this.TB_username.Text,false);

Thanks,
Alex