Mozilla Thunderbird 2.0.0.22 on Gentoo amd64 would not start.
It gives an error:
/usr/lib64/mozilla-thunderbird/mozilla-xremote-client: Error: Failed to send command: 500 command not parseable
Re-emerging world did not fix the problem.
Solution: Run Thunderbid in safe mode
$ thunderbird -safe-mode
After that Thunderbird starts OK in normal mode.