All the permissions and also the reasons why they are needed are already explained on the add-on's page (under "About this extension" at https://addons.mozilla.org/en-US/firefox/addon/reloadmatic/). There is no invasion of privacy, I keep that in high regard. The source code is also publicly visible at GitHub, so there is nothing I can hide.
Quoting to answer your question: "There are some pages that cannot be reloaded properly without adding new (unwanted) items to your browser history. This permission allows the addon to readjust your history in such cases to keep it tidy and correct."
If you feel your concerns have been addressed, please revise your vote.