I wrote a little XBL component to allow menuitems to have images centered, I added it to Firefox 2 browser context menu and worked fine immediately, after a while I installed component on Firefox 3 beta 4 and surprisingly the menuitem didn’t show the image 
I’ve asked help on Mozilla IRC and after about an hour the mistery was revealed.
The innocent CSS declaration shown below works fine on Firefox 2
.menuitem-image-center {
-moz-binding: url(‘chrome://morekomodo/content/bindings/menu.xml#menuitemImageCenterBinding’);
}
but requires a little modification on Firefox 3 beta 5pre (at this time the latest available)
.menuitem-image-center {
-moz-binding: url(‘chrome://morekomodo/content/bindings/menu.xml#menuitemImageCenterBinding’)
!important;
}
You must notice the selector without !important attribute works on Firefox 3 when applied on menus different from browser context menu.
I suspect the browser context menu should have some special treatment on new Firefox…
