Well, all I can see is a copyright notice and some acknowledgements at the bottom. Do you mean the primary navigation menu, that appears below the header?
I can see three widgets, Follow Me, the search box and Blog Sponsors.
Assuming it’s the background colour of these widgets that you want to change, then you need to change this rule:
.side-widget {
...
background-color: transparent;
background-image: url("images/bg-hatch.gif");
...
}
You should, of course, make any changes in a Child Theme, to save yourself all manner of grief later on. Child themes are trivial to create, so there’s really no excuse for not using them unless your parent theme explicitly does not support them or you’re using an old version of WP.
Having said that, you can change the background of the widgets in question by creating a new style rule in your child theme as follows:
.side-widget {
background-color: red; /* whatever colour you want */
background-image: none;
}
As for FireFox. You can’t really do Web development without FireFox, although Chrome is catching up (there is a version of FireBug – or a FireBug equivalent – for Chrome). Whatever you do, don’t use Internet Explorer.
HTH
PAE