Why does MySessions require permission X?

Read and modify bookmarks and Access browser tabs: These are key permissions because all the functionality boils down to bookmarking tabs.
Store unlimited amount of client-side data: Local browser storage is used to save the TimeLine: periodic snapshots of sessions, daily snapshots of sessions and session snapshots when the browser is closed.
Download files and read and modify the browser’s download history: This permission is used to save session backups to a file. This permission is given in this form. If only File Download could be used, then I would use it.
Access recently closed tabs: I have used this permission and am using it for experiments with the built-in session saving system, so far to no avail. I agree, in the release version - this permission is superfluous, I will remove it.