This extension doesn't report permissions clearly. To see it it's enough to compare what is stated on Ghostery extension page and what Project Insight reports: the important permission "Access your data for all websites" isn't reported explicitly, while others don't present details.
Consider use alternative listed in https://security.stackexchange.com/questions/41254/how-to-view-extension-privileges-in-firefox

Edit (after developer's response): The explanation is not really a fair justification of the omission, because the whole interface is tuned to the perception of an inexperienced user - with the exception of the most important information! The inconsistency could be easily eliminated by reporting the permission in question similarly to the rest of them (+ "Access URLs" list).
In fact, I would suggest adding elaborated explanations based on examples on https://support.mozilla.org/en-US/kb/permission-request-messages-firefox-extensions (perhaps as text displayed on demand).
Main text and stars corrected taking into consideration the developer's response.