[2018-09-03: Update to the below, having looked into it some more: When we released the extension, there was no way to achieve what the extension does without requesting permissions that would cause Firefox to display the ominous warning you object to. It has since become possible to request access to the tab only when a user interacts with the add-on. See https://developer.chrome.com/extensions/activeTab for an explanation. We have updated the add-on accordingly. But I want to stress that the add-on was never doing anything "malicious", as you suggest above. When we originally released the add-on, before the introduction of the new permission, there was simply no way to implement what we wanted without incurring that permission warning.]
Hi there, you're right that the add-on really only just appends the current tab's URL to our Push to Kindle URL when the user clicks our toolbar button. The new URL is:
https://pushtokindle.fivefilters.org/send.php?url=[current tab url]
I think the ‘read all content on all pages’ warning Firefox shows you is really just letting you know that the permissions for the extension allow us to do more than what we're currently doing. But of course we understand the concern. We certainly don't want to be giving the impression that we're reading people's content when we're not. I'm pretty certain the permissions we require for this simple add-on to function (ie. to get the tab URL of the current page you're viewing when you click our toolbar button) have always displayed this rather stark warning.
But I'm curious if with recent WebExtension developments we can now achieve the same thing without requiring the permissions that generate this warning. We'll take a look soon. If we can do it, of course we'll reduce the permissions.