Mozilla - Dynamically filling menus

I'm updating a toolbar extension for Firefox I wrote last year. I have 3 toolbarbuttons with menupopups filled dynamically. A Javascript function called by an onpopupshowing handler retrieves the contents from the internet, builds the menuitems and adds them to a menupopup at runtime. Obviously the function depends on the remote server response speed and on my internet connection. In addition, the function takes a little time to manipulate the data. In short, in my case, the process of retrieving contents and filling a menu takes about half a second, so, if I click on the toolbarbutton, a very little white rectangle is showed for a split second before the menu appears.

I'd like to delay the menu appearence but it seems quite difficult.

According to Mozilla, if we have nothing to show on a menu, we should follow the standard used in Firefox: show a single disabled item with an "(Empty)" label. If filling the menu takes a noticeable amount of time, we should not make Firefox (and users) wait for it to fill up before displaying anything. It's best to show an item with a throbber image (chrome://global/skin/icons/loading_16.png) so the user knows there's something going on, and asynchronously fill its contents.

I'm still wondering if it's possible to delay the menu appearence.

Best regards.

CGPersia toolbar for Firefox

CGPersia is a great forum dedicated to 3D arts and related softwares. CGPersia has a lot of sections and sub-sections. Since I visit CGPersia every day, I created a toolbar extension for Firefox to speed up my navigation and to easily search threads and posts.

The very early version of the toolbar is available here.
It does not contain all of the features that are planned for the final version, but it works fine for me.
Probably I will add drop-down menus with dynamic links to hottest and most  viewed threads and a window for advanced search.
I'm releasing it because a 3d passionate could find it useful.

Best regards.