First: You probably did some settings wrong with the slider or the slider is messed up because your pictures get totally skewed by it.
About your Problems:
1.: auto is not a valid value for the HTML Attribute “height” for images. Remove it completely from the image tags, and it will be sized “auto”. So, no
<img class="alignleft wp-image-78 size-full" src="http://demo.tennis-florida.com/wp-content/uploads/2014/05/summer-camp-28.jpg" alt="summer-camp-28" width="100%" height="auto" />
but
<img class="alignleft wp-image-78 size-full" src="http://demo.tennis-florida.com/wp-content/uploads/2014/05/summer-camp-28.jpg" alt="summer-camp-28" width="100%" />
2.: Internet Explorer 8 and below don’t understand HTML5 Tags like
<header></header>
<footer></footer>
and stuff. You need to use a polyfill to make it work.
Step 1: Go to https://github.com/aFarkas/html5shiv and download
https://raw.githubusercontent.com/aFarkas/html5shiv/master/dist/html5shiv-printshiv.min.js
Step 2: Save it in your theme folder.
Step 3: open your themes header.php and insert the following code in the head-section BEFORE the themes style.css:
<!--[if lt IE 9]>
<script src="https://wordpress.stackexchange.com/questions/154675/<?php bloginfo("stylesheet_directory'); ?>/html5shiv-printshiv.min.js"></script>
<![endif]-->
Step 4: Done!
Happy Coding,
Kuchenundkakao