I can't reproduce the behavior you have described. If I create a div that has scrollbars and place a dialog over the scrollbars, they do not pierce through the dialog (tested in Firefox 2.0.0.12 on Windows).

If you continue to have this problem, please re-open this ticket and provide a test page.

This problem is for Macs only. See related thread for possible fix.

The background iframe trick works for FF2/Mac as well, but currently the bgiframe plugin only handles IE6.

This patch works for me (caution: I didn't test it under IE6, and it doesn't support all the options available).

--- a/plugins/bgiframe/jquery.bgiframe.js
+++ b/plugins/bgiframe/jquery.bgiframe.js
@@ -71,7 +71,8 @@
  */
 $.fn.bgIframe = $.fn.bgiframe = function(s) {
        // This is only for IE6
-       if ( $.browser.msie && /6.0/.test(navigator.userAgent) ) {
+       if ( ($.browser.msie && /6.0/.test(navigator.userAgent)) || 
+            (/Mac/.test(navigator.platform)) && /Firefox\\/2/.test(navigator.userAgent) ) {
                s = $.extend({
                        top     : 'auto', // auto == .currentStyle.borderTopWidth
                        left    : 'auto', // auto == .currentStyle.borderLeftWidth
@@ -80,18 +81,22 @@ $.fn.bgIframe = $.fn.bgiframe = function(s) {
                        opacity : true,
                        src     : 'javascript:false;'
                }, s || {});
-               var prop = function(n){return n&&n.constructor==Number?n+'px':n;},
-                   html = '<iframe class="bgiframe"frameborder="0"tabindex="-1"src="'+s.src+'"'+
+               var prop = function(n){return n&&n.constructor==Number?n+'px':n;};
+           var html = ($.browser.msie) ? '<iframe class="bgiframe"frameborder="0"tabindex="-1"src="'+s.src+'"'+
                               'style="display:block;position:absolute;z-index:-1;'+
                                       (s.opacity !== false?'filter:Alpha(Opacity=\\'0\\');':'')+
                                               'top:'+(s.top=='auto'?'expression(((parseInt(this.parentNode.currentStyle.borderTopWi
                                               'left:'+(s.left=='auto'?'expression(((parseInt(this.parentNode.currentStyle.borderLef
                                               'width:'+(s.width=='auto'?'expression(this.parentNode.offsetWidth+\\'px\\')':prop(s.wid
                                               'height:'+(s.height=='auto'?'expression(this.parentNode.offsetHeight+\\'px\\')':prop(s.
-                                       '"/>';
+                               '"/>'
+                       : '<iframe class="bgiframe" frameborder="0" tabindex="-1" src="'+s.src+'"'+
+                       'style="display:block;position:absolute;z-index:-1;'+
+                       (s.opacity !== false?'opacity: 0;':'')+
+                'top:0;left:0;width:100%;height:100%;"/>';
                return this.each(function() {
                        if ( $('> iframe.bgiframe', this).length == 0 )
-                               this.insertBefore( document.createElement(html), this.firstChild );
+                               this.insertBefore( $(html).get(0), this.firstChild );
                });
        }
        return this;