IE9 & Drupal Form with in iFrame I know, wrap your head around it! Heh. I am having an issue in IE9 when trying to submit a form button via Drupal 7 &amp; Drupal Commerce. 

Example: http://www.um-me.com/frame.html

I have the following Drupal form source code

&lt;form class="commerce-add-to-cart commerce-cart-add-to-cart-form-8" enctype="multipart/form-data" action="/band/4/band-ninjas?fb=TRUE" method="post" id="commerce-cart-add-to-cart-form-8" accept-charset="UTF-8"&gt;
    &lt;div&gt;
        &lt;input type="hidden" name="product_id" value="8" /&gt;
        &lt;input type="hidden" name="form_build_id" value="form-oJeTHBh1Qn5myvhzMEgLvG5B6zY0vN7So0iQ4M3bazY" /&gt;
        &lt;input type="hidden" name="form_token" value="psKsdV22J3T3ybyHXCJifIVlmdjhmlIM8u8iun9WLvQ" /&gt;
        &lt;input type="hidden" name="form_id" value="commerce_cart_add_to_cart_form_8" /&gt;
        &lt;div id="edit-line-item-fields" class="form-wrapper"&gt;&lt;/div&gt;
        &lt;input type="hidden" name="quantity" value="1" /&gt;
        &lt;input type="submit" id="edit-submit" name="op" value="Add to cart" class="form-submit" /&gt;
    &lt;/div&gt;
&lt;/form&gt;


This is taken directly from Drupal. I am using it as a method to test. The actual live (also non working in IE9 version) of this is here: https://www.facebook.com/dijitl/app_187714134672420 (click the buy button)

This works in all of the other major browsers, but for some reason it does not work in IE. I have tried a "normal" non-drupal form within an iFrame and it worked fine in IE, which leads me to believe that Drupal needs something from the form that IE is not giving it.
This looks like a security problem to me.  I examined the headers being sent by IE and the session variable in the cookie doesn't appear to be getting set/transmitted.  This is because IE has strict rules about cookies in iFrames, whereas Firefox does not.  Without the session variable, your cart is not being saved.  I would take a look at this related question: https://stackoverflow.com/questions/389456/cookie-blocked-not-saved-in-iframe-in-internet-explorer and apply the solution presented there.  It should solve your problem.