The elog reads: "[...] you can create an alias in your /var/tmp/portage/mail-client/mozilla-thunderbird-bin-3.0/homedir/.bashrc. Example: alias thunderbird=thunderbird-bin". The ebuild had: "${HOME}/.bashrc" but had the whole string enclosed in double quotes, so bash expanded it. Solution: escape the $ with a \ or enclose the line in ' instead of ".
Fixed in 3.0.1 thanks for reporting.