If you're using Weechat to talk to Bitlbee to talk to FaceBook ( or other instant messaging services ), your private message window for each user will be full of notifications that the user has joined or quit.

You can get rid of most of the notifications using this filter line:

/filter add joinquitbitlbee irc.bitlbee.* irc_join,irc_part,irc_quit *

Which is specified here,

However if you do this you'll see get the "is back on server" messages; to remove those as well you want to use this line:

/filter add joinquitbitlbee irc.bitlbee.* irc_join,irc_part,irc_quit,irc_nick_back *

If you want to see those messages temporarily, for example to see if someone is online or not, enable them in Weechat with ALT and "=". Use the same key combination to remove them.