How do I turn off all presence notifications ubuntu pidgin 2.5.5?
I right-clicked "cancel presence notification" but that is only for one user, and it doesn't persist.
Presence notifications are the way that other users see your status (e.g. Online, Offline, Away) using the XMPP/Jabber protocol. Pidgin's behavior (only canceling the presence notification for the selected user) seems to make sense. Similarly, the Unsubscribe option on the same menu will stop you from being able to see their status.
However, since you tagged this question with Ubuntu, you may be talking about the notifications that pop up when users sign on, sign off, or send messages to you. These notifications are controlled through the Libnotify Popups plugin. To change these settings, go to Tools > Plugins, highlight Libnotify Popups, and click Configure Plugin. These settings should persist.