graying window after link click or loading pages

[Vladan Ionel Marius]

Binary package hint: firefox-3.5

Ubuntu release 9.10
Firefox 3.5
 Version table:
 *** 3.5.9+nobinonly-0ubuntu0.9.10.1 0
        500 http://be.archive.ubuntu.com karmic-updates/main Packages
        500 http://security.ubuntu.com karmic-security/main Packages
        100 /var/lib/dpkg/status
     3.5.3+build1+nobinonly-0ubuntu6 0
        500 http://be.archive.ubuntu.com karmic/main Packages

Normally when I click on a link in browser it loads immediately the associated page.
This firefox version for some links it behaves strange : first ALL the firefox windows become gray for 10-20 seconds, then loads the page. Same happens after a page with a link to a media file ( like playable links ) . I have the same ubuntu on another machine installed where it does not behave like that.

ProblemType: Bug
Architecture: amd64
Date: Fri Apr 23 23:59:53 2010
DistroRelease: Ubuntu 9.10
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release amd64 (20091027)
NonfreeKernelModules: nvidia
Package: firefox-3.5 3.5.9+nobinonly-0ubuntu0.9.10.1
ProcEnviron:
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-20.58-generic
SourcePackage: firefox-3.5
Uname: Linux 2.6.31-20-generic x86_64