IE & Firefox browser don't display like Chrome

https://www.nedab.org — is the page I’m working on.
2.3.4 is the version I have loaded. Looks great in Chrome & Safari; horrible in IE & Firefox. I want the background color to the text area of pages to be White. I can’t find that setting. I must have changed in in style-sheets for Chrome, didn’t impact IE or Firefox. and 2) The Primary Navigation – great in Chrome (reads across top of main text area on all pages) but in IE & Firefox they appear as an underlined list (looks bad). Last is the spacing between menu items. I’m using Custom Menus in the side-bars with the pages I want people to be able to navigate to easily