Php – external js & css not loading in codeigniter

To load external Javascript file in codeignitor, I'm using

<script src="<?php echo base_url("application/js/contentslider.js"); ?>" type="text/javascript"></script>

I can see in the page's source as

<script src="http://localhost/cinifb_ci/application/js/contentslider.js" type="text/javascript"></script>

which means to my knowledge that the file is loading perfectly similarly for my CSS file, I've used

<link rel="stylesheet" href="<?php echo base_url(); ?>application/css/default.css" type="text/css" />

and in the page's source code its showing as

<link rel="stylesheet" href="http://localhost/cinifb_ci/application/css/default.css" type="text/css" />

which means even its loading perfectly. (on clicking the external js/css link in the source its showing 403 Forbidden). But neither of their effects are applied on the page. No error its showing.
I've loaded URL helper in controller as $this->load->helper('url');

and placed $autoload['helper'] = array('url'); in autoload.php

can you please explain me where I went wrong.

I learn that to load external JS, we need to install jquery-codeigniter library. I've downloaded them and included the respective files into respective similar folders of my application folder.

Now when I try to include $this->load->library('jquery'); in my controller, its showing

An Error Was Encountered

Unable to load the requested class: jquery

Hence I request you to please help me to understand why 403 Forbidden is showing when I can see its pointing to the exact location of the JS/CSS file and secondly if the installation of the jquery-codeigniter library is wrong please guide me.
Note: http://ellislab.com/codeigniter/user-guide/libraries/javascript.html didn't help me

Edit:
jquery-codeigniter library i've placed in system/libraries/javascript/

In systems .htaccess file, I've written as

RewriteEngine on
RewriteRule ^$ /index.php [L]
RewriteCond $1 !^(index\.php|images|css|js|video_files|robots\.txt|favicon\.ico)
RewriteRule ^(.*)$ /cinifb_ci/index.php/$1 [L]

In the view I'm writing as

$this->load->helper('url');
<script src="<?php echo base_url("application/js/jquery-1.8.2.js"); ?>" type="text/javascript"></script>

In controller as

$this->load->helper('url');
$this->load->library('javascript');
$this->load->library('javascript/jquery');
$this->load->library('Jquery_ext');

again if I look at source its pointing to correct source but still if i click external js file link, its showing 403 Forbidden error
Sorry for lengthy post 🙁
Suggestions please ..!