Comment 74 for bug 222208

P.S. For Thunderbird trunk (which should be fixed first) it is of course comm-central, http://hg.mozilla.org/comm-central/ and rather than clone (which might use a lot of time and bandwidth) you may prefer to install a bundle, see
http://benjamin.smedbergs.us/blog/2008-06-05/getting-mozilla-central-with-limited-bandwidth/ (mutatis mutandis for comm-central vs. mozilla-central)
https://developer.mozilla.org/En/Developer_Guide/Source_Code/Mercurial#Bundles