navigation web menu

[Gourouvin Laurent]

I have some bugs with Ubuntu and Firefox 4.0.1.
In a a website, i use their menu with css. The first tabs contains four items.
But I can't use the 3 or 4 items because the menu that immediately closes

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: firefox 4.0.1+build1+nobinonly-0ubuntu0.11.04.1
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic i686
NonfreeKernelModules: nvidia
Architecture: i386
Date: Wed May 11 23:16:10 2011
FirefoxPackages:
 firefox 4.0.1+build1+nobinonly-0ubuntu0.11.04.1
 flashplugin-installer N/A
 adobe-flashplugin N/A
 icedtea-plugin N/A
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Release i386 (20101007)
ProcEnviron:
 LANGUAGE=fr_FR:en
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: firefox
UpgradeStatus: Upgraded to natty on 2011-05-07 (4 days ago)