External links do not change focus to Firefox

Binary package hint: firefox

I just upgraded from Ubuntu 10.10 with Firefox 3.5 to Ubuntu 11.04 with Firefox 4.0.1. After the upgrade, external links do not change focus to Firefox. For example, when I click on a link in Thunderbird then the link is loaded in a new tab in Firefox, however, the focus does not change to the Firefox window. This is especially annoying if the Firefox window is covered by another window since I am then unable to see the new link in the Firefox tab until I manually change the focus by clicking on the Firefox window.

OS Version: Ubuntu 11.04
Firefox Version: 4.0.1

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: firefox 4.0.1+build1+nobinonly-0ubuntu0.11.04.2
ProcVersionSignature: Ubuntu 2.6.38-8.42-generic 2.6.38.2
Uname: Linux 2.6.38-8-generic x86_64
NonfreeKernelModules: nvidia
Architecture: amd64
Date: Tue May 24 17:07:08 2011
ExecutablePath: /usr/lib/firefox-4.0.1/firefox-bin
FirefoxPackages:
 firefox 4.0.1+build1+nobinonly-0ubuntu0.11.04.2
 flashplugin-installer 10.3.181.14ubuntu0.11.04.1
 adobe-flashplugin N/A
 icedtea-plugin N/A
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release amd64 (20100429)
ProcEnviron:
 LANGUAGE=en_US:en
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: firefox
UpgradeStatus: Upgraded to natty on 2011-05-19 (4 days ago)