That appears in the Console tab of Firebug.
Then, after a few minutes, this error randomly came up when I wasn’t interacting with the page.
Error: Permission denied to access property ‘toString’
slice.call( docElem.childNodes, 0 )[0].nodeType; jQuery.js (line 3811)
Oh dear!
So, I’ve no idea about the second error, but let’s deal with the first one first.
What FF is telling you is that it cannot find the file at http://localhost/lightbox_ajax/emailtester.php
This might be an obvious question, but let’s exclude it anyway.
Does the file emailtester.php exist in the folder C:/xampp/htdocs/lightbox_ajax/ ?
emailtester.php does exist in a folder, “Scripts”, that it is located in C:/xampp/htdocs/lightbox_ajax/Scripts/emailtester.php I’ll copy it to the root folder and see what happens.
That’ll be the problem 
In my version it needs to be in the same folder as index.html.
Let me know if it works …
Ah-HA! That’s it. It worked when I copied it into the folder up one level. AWESOME.
Excellent!! Well done!!
Now you can have a working basis, you can hopefully work from that and adapt everything else to work the way you want.
Regarding the HTML and CSS on your page, I would like to point you back in the direction of RonPat if you have any further questions.
He certainly knows his stuff, so just jump back in to the thread you guys had in the CSS forum.
If you have any more JS questions, just let me know.
The next part should be easier since I have a better understanding of how the ajax request works and how to maneuver the JS functions a bit better. The only thing is that I will need to pass an array with the second form data I’m guessing (I saw that you did that with your other example in this same thread, so I’ll try to model it off that).
Most of the PHP validation script for the 2nd form is done including a mailer and a database writer using PHP Data Objects, though I’ll need to make sure it’s set up correctly.
I also am considering adding an anti-spam measure in there with a few random characters for the user to input. Maybe that’s overkill though, and I can do something more simple (users may hate putting in random chars just to join my list).
That all sounds quite doable.
Regarding the anti-spam measure, you might want to check out this thread where it is discussed quite thoroughly: http://www.sitepoint.com/forums/showthread.php?934299-Simple-PHP-math-captcha-to-minimize-bots-sending-you-junky-emails