A new issue: after forcing the n-th password change on me, Facebook now won't let me login via Miranda. I bet this issue is already known by Ghazan and the other developers working on the FB plugin, but I am sending the very small netlog to @ghazan, just in case.
EDIT (addition)
The previous issue (no login via Miranda) has been solved. It wasn't Miranda's problem. I had to reset the password, because FB wouldn't let me log in by any browser. Maybe Miranda just triggered the problem? It is a possibility, because it happened right after an update, but the problem was general.
About lost messages in history:
Some messages are still retrospectively missed after the fact, even if I have "load last messages on opening message windows" set to 99 (max). I am not able to understand in which conditions this happens (it's not everytime, just sometime). Ok, this is not new.
But I do have some new information: it appears that the messages containing a quote are systematically missed by Miranda, not only in history after the fact: the messages are missed even if Miranda is online and the window is open when the message arrives.