I have a PHP script on my server which reads cookie and then redirects user to my order form. I do not want this script be visited by the robots, such as googlebot or msn bot, so I use the following robots.txt:
User-agent: * Disallow: /folder/redirect.php
My question is, since IE and Firefox are agents, will this robots.txt also block web visitors?
Robots.txt does not "block" anything. Compliance is voluntary.
Good robots will read your robots.txt file and stay out.
Browsers are not robots. They won't read your robots.txt file before fetching a page, so it will not affect them.
Bad robots may read your robots.txt file and ignore it, or they might not read your robots.txt file at all.
In order to block bad robots, you need something that actually denies them access to your pages, rather than a robots.txt file that asks them nicely to stay out. Apache users can use mod_rewrite to enforce access restrictions, along with several other methods, and IIS users can use the optional ISAPI Rewrite package (purchased separately) to do much the same thing.