I know you are getting a huge list of FF3 problems so I thought I would add to the pile .

FF3 now correctly respects z-indexes... yay ff3! Although, it looks like Ext has been depending on this z-index bug.

I am not sure how Ext decides what z-index to use but something needs to be fixed. I am masking a particular panel using:

panel.getEl().mask();

The z-index of the mask comes out to be 20,000. The z-index of a dialog that is open is 9,012. So, the mask of this particular panel appears in front of the dialog.

Perhaps element.mask() needs to bubble up the dom tree checking to see if it has a parent with a z-index. If so, then the mask's z-index just needs to be a little higher than that. If a parent doesn't have a z-index then the masks's z-index should be at some small value.

Here is a quick patch that does this. Pardon the messy code.

Ext.override(Ext.Element, {
     
    findParentBy : function(callback, returnEl){
         var p = this.dom, b = document.body, dq = Ext.DomQuery;
         while(p && p.nodeType == 1 && p != b){
             if(callback(p, this)){
                 return returnEl ? Ext.get(p) : p;
             }
            p = p.parentNode;
         }
         return null;
     },
    
    mask : function(msg, msgCls){
         if(this.getStyle("position") == "static"){
            this.setStyle("position", "relative");
         }
         if(this._maskMsg){
            this._maskMsg.remove();
         }
         if(this._mask){
            this._mask.remove();
         }

        this._mask = Ext.DomHelper.append(this.dom, {cls:"ext-el-mask"}, true);
        
        //-------------
        var p = Ext.fly(this.dom.parentNode, '_internal');
         var parentZIndex = p.findParentBy(function(parent){
             var zIndex = Ext.fly(parent).getStyle("z-index");
             return  zIndex != "auto" && zIndex != null;
         }, true);
         if(parentZIndex)
            this._mask.setStyle("z-index", parentZIndex.getStyle("z-index")+1);
         else 
            this._mask.setStyle("z-index", 100);
        //--------------
        
        this.addClass("x-masked");
        this._mask.setDisplayed(true);
         if(typeof msg == 'string'){
            this._maskMsg = Ext.DomHelper.append(this.dom, {cls:"ext-el-mask-msg", cn:{tag:'div'}}, true);
             var mm = this._maskMsg;
            mm.dom.className = msgCls ? "ext-el-mask-msg " + msgCls : "ext-el-mask-msg";
            mm.dom.firstChild.innerHTML = msg;
            mm.setDisplayed(true);
            mm.center(this);
         }
         if(Ext.isIE && !(Ext.isIE7 && Ext.isStrict) && this.getStyle('height') == 'auto'){ // ie will not expand full height automatically
            this._mask.setSize(this.dom.clientWidth, this.getHeight());
         }
         return this._mask;
     }
    
 });