Thunderbird - improvement - sorting of messages

TB sorts messages according to the selected attribute (column).
Unfortunately, currently initial sequence of messages with equal
sort keys isn't preserved during the sort operation. Since there's
no possibility to create composite key ( ;-) ) there's no way to
sort messages according to a complex criterion.

I would like to have an option for sort: "preserve the initial
sequence of messages with equal keys". It would allow to have
messages sorted according to composite key by use of sequence of
sort ops.

As it could (in some cases) result in much slower sorting ops it
should be an optional setting available from main screen (not via
Troubleshooting Information>Important Modified Preferences).

witrak()