Move append_output animation height lock release into timeout.

IPython/html/static/notebook/js/outputarea.js

@@ -293,14 +293,18 var IPython = (function (IPython) {
         
         this.outputs.push(json);
         
+        // We must release the animation fixed height in a timeout since Gecko
+        // (FireFox) doesn't render the image immediately as the data is 
+        // available.
+        var that = this;
+        setTimeout(function(){
         // Only reset the height to automatic if the height is currently
         // fixed (done by wait=True flag on clear_output).
         if (needs_height_reset) {
-            this.element.height('');    
+                that.element.height('');    
         }
-
-        var that = this;
-        setTimeout(function(){that.element.trigger('resize');}, 100);
+            that.element.trigger('resize');
+        }, 250);
     };