This add-on is able to "Access your data for all websites".

From Mozilla (support.mozilla .org /en-US/kb/permission-request-messages-firefox-extensions?as=u#w_access-your-data-for-all-websites):

"The extension could read the content of any web page you visit, as well as data you enter into those web pages, such as usernames and passwords.

Extensions requesting this permission might:

Read product and price information from a page to help find you the best price on items you're shopping for
Offer a password manager that reads and writes details of your username and password
Provide an ad blocker by reading the content of each web page you open to find and remove ad code"

There is absolutely zero reason this add-on should be reading everything about your web browser.

Avoid this.