Why isn't this working in Firefox?

Hi.

I've been developing my site for a few months and its getting pretty near where I want it to be.

I'm currently converting pages from my old design to a new one, including a new external CSS.

One page, which is heavy with javascript, is giving me problems because it won't display as it should when viewed in Firefox. IE works out the corrrect layout but I am aware that IE is good at overlooking bad coding an delivering what it thinks the coder intended; whereas firefox is a bit more strict with its compliance.

The page in question is here

If you view in IE you'll see that the recent blog entries div (div id=blog) should be below the expanding div (div id=below_thisText2), but in firefox it gets shoved to the top of the right-floated container that holds the navigation, promo and links.

can anyone tell me why please?

Here is the external style sheet:

.style1 {
font-size: small;
}
.style5 {font-size: 10px}
.style6 {
color: #C49248
}
body {
font-family: Verdana, Geneva, Arial, helvetica, sans-serif;
background-color: #000000;
color: #CAAB4E;
text-decoration: none;
}
a:link {
color: #C49248;
text-decoration: none;
}
a:visited {
color: #896D2A;
text-decoration: none;
}
a:hover {
color: #FAF4E9;
text-decoration: none;
}
a:active {
color: #C49248;
text-decoration: none;
}
#main_container {
width: 820px;
margin-right: auto;
margin-left: auto;
background-image: url(portal/assets/images/container_background_800_wide.gif);
background-repeat: no-repeat;
margin-top: 20px;
}
#main_container_home {
width: 820px;
margin-right: auto;
margin-left: auto;
height: 950px;
}

#main_container_links {
height: 950px;
width: 820px;
margin-right: auto;
margin-left: auto;
}
#main_container #right_container {
height: auto;
width: 200px;
float: right;
}

#main_container #right_container #nav {
height: 220px;
width: 140px;
font-family: Georgia, "Times New Roman", Times, serif;
font-size: large;
background-image: url(portal/assets/images/nav_background/nav_background.png);
background-repeat: no-repeat;
padding-top: 40px;
padding-right: 30px;
padding-bottom: 40px;
padding-left: 30px;
text-decoration: none;
color:  #FFFFCC;
}
#main_container  #right_container  #nav a:link  {
color: #FFFFCC;
}
#main_container #right_container #nav a:hover {
color: #C49248;
}
#main_container #right_container #nav a:visited {
color: #FFFFCC;
}

#main_container #right_container #promo {
height: 270px;
width: 180px;
padding: 10px;
}
#main_container #right_container #links {
height: 350px;
width: 100%;
font-size: small;
text-align: center;
}


#main_container #left_container {
width: 590px;
float: left;
padding: 5px;
}
#main_container  #left_container  #content_home  {
height: 740px;
width: 590px;
background-image: url(portal/assets/images/content_backgrounds/content_home_home%20copy.png);
background-repeat: no-repeat;
}
#main_container #left_container #content_links {
height: 740px;
width: 590px;
background-image: url(portal/assets/images/content_backgrounds/content_links_links%20copy.png);
background-repeat: no-repeat;
color: #000000;
font-family: "Courier New", Courier, monospace;
}
#main_container #left_container #content_about {

height: auto;
width: 590px;
background-image: url(portal/assets/images/content_backgrounds/content_about_aboutme%20copy.png);
background-repeat: no-repeat;
color: #000000;
font-family: "Courier New", Courier, monospace;
}
#main_container #left_container #content_links #upper_links #links_research {
float: left;
width: 250px;
padding-left: 30px;
padding-top: 30px;
padding-right: 15px;
padding-bottom: 15px;
color: #000000;
}
#left_container a:link {
font-size: small;
color: #000000;
text-decoration: none;
}
#left_container a:active {
font-size: small;
color: #333333;
text-decoration: none;
}
#left_container a:visited {
font-size: small;
color: #333333;
text-decoration: none;
}
#left_container a:hover {
font-size: small;
color: #CC9933;
text-decoration: none;
}
#main_container #left_container #content_links #upper_links #links_Recommendations {
float: right;
width: 250px;
padding-top: 30px;
padding-right: 15px;
padding-bottom: 15px;
padding-left: 30px;
color: #000000;
}

#main_container #left_container #main_site_title {
background-image: url(portal/assets/images/main_title.gif);
background-repeat: no-repeat;
height: 200px;
width: 100%;
}
#main_container #left_container #page_title {
height: 100px;
width: 100%;
text-align: center;
vertical-align: middle;
}
#main_container #left_container #upper_home {
height: 200px;
width: 90%;
font-size: medium;
background-repeat: no-repeat;
background-position: right bottom;
padding: 15px;
color: #000000;
margin-top: 0px;
margin-right: 15px;
margin-bottom: 0px;
margin-left: 15px;
text-align: center;
font-family: Georgia, "Times New Roman", Times, serif;
text-decoration: none;
}
#main_container #left_container #upper_links {
height: 550px;
}
#main_container #left_container #content_about #about_top_text {
font-size: small;
width: 92%;
padding-top: 1%;
padding-right: 4%;
padding-bottom: 1%;
padding-left: 4%;
height: 230px;
}

#main_container #left_container #upper_about {

height: 180px;
}
#main_container #left_container #upper_about_left {
float: left;
width: 46%;
padding-top: 1%;
padding-right: 3%;
padding-bottom: 3%;
padding-left: 0%;
height: auto;
}
#main_container #left_container #upper_about_right {
float: right;
width: 46%;
padding-top: 1%;
padding-right: 3%;
padding-bottom: 3%;
padding-left: 0%;
height: auto;
}
#main_container #left_container #lower_home {
height: 200px;
width: 510px;
background-image: url(portal/assets/images/promo/free_sample_promo%20copy.png);
background-repeat: no-repeat;
background-position: center top;
padding-top: 200px;
padding-right: 40px;
padding-left: 40px;
text-align: center;
color: #000000;
padding-bottom: 0px;
}
#main_container #left_container #lower_links {
height: auto;
padding-top: 0px;
padding-right: 30px;
padding-bottom: 15px;
padding-left: 30px;
}
#main_container #left_container #lower_about {
height: auto;
width: 92%;
text-align: center;
padding: 4%;
font-size: small;
}
#main_container #main_container_about #left_container #content_about #above_thisText2 {
background-image: url(portal/assets/images/content_backgrounds/scroll_repeat/scroll_top_long.png);
height: 47px;
width: 600px;
margin-top: 20px;
}
#main_container #main_container_about #left_container #content_about #below_thisText2 {
background-image: url(portal/assets/images/content_backgrounds/scroll_repeat/scroll_bottom_long.png);
height: 33px;
width: 600px;
margin-bottom: 20px;
}

#main_container #main_container_about #left_container #content_about #thisText2_container {
color: #000000;
font-size: small;
background-image: url(portal/assets/images/content_backgrounds/scroll_repeat/scroll_middle_long.png);
background-repeat: repeat;
height: auto;
width: 530px;
padding-right: 35px;
padding-left: 35px;
padding-bottom: 15px;
}


#main_container #left_container #shouts_container {
height: 47px;
width: 600px;
background-image: url(portal/assets/images/content_backgrounds/scroll_repeat/scroll_top_long.png);
background-repeat: no-repeat;
}

#shouts_left	{
height: 33px;
width: 600px;
background-image: url(portal/assets/images/content_backgrounds/scroll_repeat/scroll_bottom_long.png);
}
#shouts_centre	{
padding: 5px;
height: auto;
width: 190px;
float: left;
}
#shouts_right	{
padding: 5px;
height: auto;
width: 190px;
float: left;
}

#footer_container {
width: 800px;
margin-right: auto;
margin-left: auto;
}
#footer {
height: 180px;
width: 100%;
background-image: url(portal/assets/images/new_footer_800_wide.jpg);
background-repeat: no-repeat;
background-position: bottom;
padding-bottom: 20px;
}
#footer  #blog  {
height: 100%;
width: 70%;
font-size: small;
overflow: hidden;
}

#textnav {
height: 100px;
width: 100%;
text-align: center;
}

Thanks for any help ;-)

Phil.

p.s. I've also attached the CSS seperately.

new_portal.css