Looks like an interesting extension, but unfortunately I would never install it given that "this add-on can access data for all your websites". As far as I am aware, this means it can read and record all data in all websites I visit (including emails, banks, etc) and record everything I type anywhere (including usernames and passwords). Even if the extension's source code is available on GitHub, there is no guarantee…
Basically, if the addon wants to interact with any kind of urls, this message is unavoidable. Which means that even if the addon doesn't require to access any data of the websites, as long as it wants to be triggered for any websites, this message is not going to be avoidable.
https://extensionworkshop.com/documentation/develop/request-... has more information.