correct HTTP header for json file

I've searched around and found two different ways to define Content-type for JSON file loaded with php.

HTTP authentication logout via PHP

What is the correct way to log out of HTTP authentication protected folder?

.htaccess r=301 vs r=302

I am creating rules in my .htaccess for mobile, or bad pages etc...

Is there any need to sanitize a $_POST value before using it in a PHP header (for redirecting)

Can I use a posted value in a PHP redirect header safetly without checking it:

Handling PUT/DELETE arguments in PHP

I am working on my REST client library for CodeIgniter and I am struggling to work out how to send PUT and DELETE arguments in PHP.

Resource interpreted as document but transferred with MIME type text/css

Resource interpreted as document but transferred with MIME type text/css

This is the error that's showing up in Google Chrome Inspector.

Email Tracking - GMail

I am creating my own email tracking system for email marketing tracking. I have been able to determine each persons email client they are using by using the http referrer but for some reason GMAIL does not send a HTTP_REFERRER at all!

Prevent Back button from showing POST confirmation alert

I have an application that supplies long list of parameters to a web page, so I have to use POST instead of GET. The problem is that when page gets displayed and user clicks the Back button, Firefox shows up a warning: