Sometime on Oct 8, RMP cobbled together some glyphs to say:
know how exactly mozilla does threading, but it did not mess the threading even when the "Re" was missing in the Subject.
Umm, no mail client should do threading based on subject. Mail clients are supposed to use the Message-Id, In-Reply-To:, and References: mail headers to identify the thread that a mail belongs to. Subject: can be used to guess, but should not be the primary means.
Philip