I logged into facebook messenger on Pidgin. Now for about an hour afterwords I get endless notifications of people coming "online" on facebook. I can't find any option to disable this, but it's a real nuisance. They are the built in "Unity" ubuntu notifications. "John Smith is Online" it says over and over and over again
Go into the pidgin main window and open the tools menu, add-ons and a new window opens showing the add-ons.
Search for the lib.notify entry and there you can disable to show logins/logouts.
It is not recommended to disable the plugin itself, at least if you do not care about the message indicator integration.