ooo, dude! i so found it out!!!
. sad though, that the mozilla people made it so hard to figure it out!!! i do expect more user friendly stuff.
and here it comes:
1. tools -> options -> display -> fonts (bottom, right) -> UNselect "apply the default character encoding to all incoming messages" checkbox. -> ok
2. view -> character encoding -> auto-detect -> universal
there you go! without restarting, thunderbird does nothing, which is most irritating. you do expect thunderbird to be able to set stuff like this without having to restart.
anyway... now my thunderbird is able to detect and view for example cyrillic windows encoding, windows default encoding, utf-8, etc. etc. i am so happy!!!