At my office we use Microsoft Office Communicator, but as a fervent user of Pidgin I’m still having issues with using our Microsoft Office Communicator account.
The bug is (of course) on the Microsoft-side, not Pidgin-sipe, Pidgin nor NSS. Pidgin does’t have an API to disable NSS security fix per plugin/SSL connection, so this can’t be implemented in the plugin (yet).
So this is a workaround for a usable solution:
Now there’s way to go to Lync – but that will work better – except from video/audiocalling (still not available from now).