addon domain accessing in browser

As cpanel treats addon domain as a subdomain for main account so it is accessed in browser as a subdomain but if you  want to access the addon domain in browser as :

http://addondomain

and not as as sudomain like :

http://maindomain/addon domain.

then you needs to create a .htaccess and define below rules:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTP_HOST} main-domain\.com$
RewriteRule ^(.*)$ "http\:\/\/www.another-domain\.com\/" [R=301,L]
</IfModule>

Replace your respective main domain and addon domains in .htaccess file.