IE CSS issues;

I have a site @ https://www.weedshopinc.com On that site i have some IE issues and believe it or not, some firefox2 issues. Let me start with IE issues:
In the boxes on the front page, you will see text like "News" and "Member Login". I have an image that creates the color behind that text in the boxes. Notice how the color (image) does not stretch to the right side of the box. It stops short in IE. In firefox2, that is not seen. Here is the CSS for those colors (images):

.box_header {
font-size:15px;
margin:0;
padding:4px;
background:url("//weedshopinc.com/wp-content/themes/black-minimalism-10/images/MTwG.jpg");
background-repeat:repeat-x;
font-weight:bold;
color:#333333;
}

This next one happens in both firefox2 and IE (i will file it under IE):
In the "member login" box, notice the signup pic/button; now notice the border around the pic/button. This does not have a border around it in the image. The image can be found here:
https://www.weedshopinc.com/product-category/weed-strains/ .png
and here is the code for that image:

There is no CSS for this.
In the same box but a firefox2 issue: under Start your free blog today; notice the green checkmarks. In IE these display further to the right but in firefox2 they display wonky. Here is the CSS for that:

.checkmark-right ul {
list-style-image: url(images/checkmarksm.jpg);
float: right;
padding: 5px;

I thank you for your help