The error I supect maybe related to “xulrunner” since upgrading my firefox also implies upgraded my xulrunner version to xulrunner-2.0.1-1.
THE SOLUTION then was to: downgrade packages, reverting back my firefox to firefox-4.0-1 and my xulrunner-2.0.1 solved the problem.
Going to /var/cache/pacman/pkg is always my friend since almost all of my old/older version of packages are stored in this directory.
$ cd /var/cache/pacman/pkg
$sudo pacman -U xulrunner-2.0.1-i686.pkg.tar.xz
$sudo pacman -U firefox-4.0-1-i686.pkg.tar.xz
then rerun my firefox and back to normal!
No upgrade for Firefox for now using pacman. =)Tweet