All these permissions are needed to let the extension works properly. I deleted exaggerated permissions since the comment that you mentioned. And I said that in comments but moderator of the site deleted the user comment with my answer. :)

If you worry about security and if you think that the extension that works locally can some how make a harm then you can use the extension without an installation as I described in the extension description. In the case the extension will be executed in a Firefox sandbox as a usual local HTML page.

I know that the code of the extension is not an ideal and I am going to improve it as soon as I have time. Now the extension works and does what It should. :)

Well, so many questions about these useless permissions :) I think I should add some info about it to the description.