> Curious-why open an addon in a new tab?
When I wrote this extension many years ago, I wanted to only enable it when I wanted to edit cookies, which is rarely.
When I published the add-on to Firefox, the initial use case is Firefox for Android, which does not have an extension button (as of Firefox 55, it is possible).

In version 1.3, I have added an option to not automatically open the add-on upon startup, and also an extension button to quickly access the cookie manager via the extension button.

3) The add-on is functional, but the UI is not really that strong. I expect the UI to be improved in one of the next versions, so I haven't published a screenshot yet.

> If you want feedback (...) maybe setup a support page
I have published the source code on Github, together with an issue tracker @ https://github.com/Rob--W/cookie-manager/issues