One of the best things about Mozilla Thunderbird is that it runs on a variety of operating systems. Another is that its extensions are also cross-platform, so if you switch operating systems (say, from Windows XP to Ubuntu Linux), you can simply re-install the extensions you know and love.
I decided I might as well take the opportunity to try out a few new extensions. One of those I plan on keeping is Christian Weiske's "Display Mail User Agent" extension, because it makes harassing people who are using Outlook easy as pie. It looks cool, too.
While my old extensions work perfectly, my character encoding did not. Messages encoded in UTF-8 (for worldwide compatibility, in case I decide to write in Sanskrit or something) displayed in a different font. After much brow-wrinkling, I found a blog post that described the problem, and provided a solution. Then I realized that the problem was already solved by Thunderbird's Preferences dialog (as I describe in this comment in Bugzilla), albeit in a hard-to-find manner.