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.

I guess I should answer here. :) I think that permission system of Mozilla's addons is useless. It's possible to do something bad with almost any of these permissions. And a people who will check permissions before clicking "Yes" are just paranoids. I mean nobody will check permissions except few people even if we speak about software developers. All what this system does is spend software developer time. Checking security of addons is Mozilla's job not users.

If I have enough time I will fix this and delete exaggerated permissions.