Hi there! As product manager for this extension, I can categorically assure you that we have no intention at all in displaying advertisements. It would wreck the user experience and call forth exactly the kind of indignation I sense from your comment here :)

The notification permission is used for communicating status messages, such as displaying errors when Mendeley Web Importer cannot import a document. We may potentially use it also in future to indicate that uploads have finished.

I hope you have been enjoying using Mendeley Web Importer and will continue to benefit from it.