In the end of February 2013, after an update suddenly Firebird couldn't play flash anymore. The browser mentioned to install the latest Adobe flash Player so I was redirected to the Adobe download page where I could download the Adobe Flash Player 11.2 for my Ubuntu 11.10 distro.
After a fresh install of Firefox and THunderbird on Ubuntu Natty the colors of indexed images and icons are mangled.
Jena said on this page http://ubuntuforums.org/showthread.php?t=1742738
Re: (some) colors shifted after Natty upgrade
Also, I checked on another computer - the screenshots I posted above are accurate. Those are really the colors it shows.