Problem
Due to the code used in \Snippets\FastCartThickBoxContent.html, the checkout button image path in FastCart is pointing to the mobile template path, which results in a broken checkout button image.
<img src="%%GLOBAL_IMG_PATH%%/%%GLOBAL_SiteColor%%/CheckoutButton.gif" alt="" />
Below is the result of Firefox Android
Solution
The easiest fix is to copy “CheckoutButton.gif” from the Desktop template to the mobile template