How to fix Spry Menu bar and Firefox with a Mac

Question

The spry menu bar does not properly display in Firefox (Version11&12) on a mac. Have looked at a number of different ways to fix this. Included is a copy of css for menu bar. Would appreciate any suggestions.
/* The outermost container of the Menu Bar, an auto width box with no margin or padding */
ul.MenuBarHorizontal
          margin: 0;
          padding: 0;
          list-style-type: none;
          font-size: 100%;
          cursor: default;
          width: auto;
/* Set the active Menu Bar with this class, currently setting z-index to accomodate IE rendering bug: http://therealcrisp.xs4all.nl/meuk/IE-zindexbug.html */
ul.MenuBarActive
          z-index: 1000;
/* Menu item containers, position children relative to this container and are a fixed width */
ul.MenuBarHorizontal li
          margin: 0;
          padding: 0;
          list-style-type: none;
          font-size: 100%;
          position: relative;
          text-align: left;
          cursor: pointer;
          width: 11em;
          float: left;
/* Submenus should appear below their parent (top: 0) with a higher z-index, but they are initially off the left side of the screen (-1000em) */
ul.MenuBarHorizontal ul
          margin: 0;
          padding: 0;
          list-style-type: none;
          font-size: 100%;
          z-index: 1020;
          cursor: default;
          width: 11em;
          left: -1000em;
          position: relative;
/* Submenu that is showing with class designation MenuBarSubmenuVisible, we set left to auto so it comes onto the screen below its parent menu item */
ul.MenuBarHorizontal ul.MenuBarSubmenuVisible
          left: auto;
/* Menu item containers are same fixed width as parent */
ul.MenuBarHorizontal ul li
          width: 11em;
          float: none;
/* Submenus should appear slightly overlapping to the right (95%) and up (-5%) */
ul.MenuBarHorizontal ul ul
          position: absolute;
          margin: -5% 0 0 95%;
/* Submenu that is showing with class designation MenuBarSubmenuVisible, we set left to 0 so it comes onto the screen */
ul.MenuBarHorizontal ul.MenuBarSubmenuVisible ul.MenuBarSubmenuVisible
          left: auto;
          top: 0;
DESIGN INFORMATION: describes color scheme, borders, fonts
/* Submenu containers have borders on all sides */
ul.MenuBarHorizontal ul
          /* [disabled]border: 1px solid #CCC; */
/* Menu items are a light gray block with padding and no text decoration */
ul.MenuBarHorizontal a
          display: block;
          cursor: pointer;
          background-color: #FFFFCC;
          padding: 0.5em 0.75em;
          color: #4F8627;
          text-decoration: none;
/* Menu items that have mouse over or focus have a blue background and white text */
ul.MenuBarHorizontal a:hover, ul.MenuBarHorizontal a:focus
          background-color: #FFFFCC;
          color: #4F8627;
/* Menu items that are open with submenus are set to MenuBarItemHover with a blue background and white text */
ul.MenuBarHorizontal a.MenuBarItemHover, ul.MenuBarHorizontal a.MenuBarItemSubmenuHover, ul.MenuBarHorizontal a.MenuBarSubmenuVisible
          background-color: #FFFFCC;
          color: #4F8627;
SUBMENU INDICATION: styles if there is a submenu under a given menu item
/* Menu items that have a submenu have the class designation MenuBarItemSubmenu and are set to use a background image positioned on the far left (95%) and centered vertically (50%) */
ul.MenuBarHorizontal a.MenuBarItemSubmenu
          background-image: url(SpryMenuBarDown.gif);
          background-repeat: no-repeat;
          background-position: 95% 50%;
/* Menu items that have a submenu have the class designation MenuBarItemSubmenu and are set to use a background image positioned on the far left (95%) and centered vertically (50%) */
ul.MenuBarHorizontal ul a.MenuBarItemSubmenu
          background-image: url(SpryMenuBarRight.gif);
          background-repeat: no-repeat;
          background-position: 95% 50%;
/* Menu items that are open with submenus have the class designation MenuBarItemSubmenuHover and are set to use a "hover" background image positioned on the far left (95%) and centered vertically (50%) */
ul.MenuBarHorizontal a.MenuBarItemSubmenuHover
          background-image: url(SpryMenuBarDownHover.gif);
          background-repeat: no-repeat;
          background-position: 95% 50%;
/* Menu items that are open with submenus have the class designation MenuBarItemSubmenuHover and are set to use a "hover" background image positioned on the far left (95%) and centered vertically (50%) */
ul.MenuBarHorizontal ul a.MenuBarItemSubmenuHover
          background-image: url(SpryMenuBarRightHover.gif);
          background-repeat: no-repeat;
          background-position: 95% 50%;
BROWSER HACKS: the hacks below should not be changed unless you are an expert
/* HACK FOR IE: to make sure the sub menus show above form controls, we underlay each submenu with an iframe */
ul.MenuBarHorizontal iframe
          position: absolute;
          z-index: 1010;
          filter:alpha(opacity:0.1);
/* HACK FOR IE: to stabilize appearance of menu items; the slash in float is to keep IE 5.0 from parsing */
@media screen, projection
          ul.MenuBarHorizontal li.MenuBarItemIE
                    display: inline;
                    f\loat: left;
                    background: #FFF;

Answer 1

Change
ul.MenuBarHorizontal ul
          margin: 0;
          padding: 0;
          list-style-type: none;
          font-size: 100%;
          z-index: 1020;
          cursor: default;
          width: 11em;
          left: -1000em;
          position: relative;
to
ul.MenuBarHorizontal ul
          margin: 0;
          padding: 0;
          list-style-type: none;
          font-size: 100%;
          z-index: 1020;
          cursor: default;
          width: 11em;
          left: -1000em;
          position: absolute;
Gramps