Bienvenue, hope that's correct translation for 'welcome'.

Thanks a lot for taking a step farther :) , I am still struggling to get this enabled on addons.mozilla.org (ironically)

Yes you are right, I was being optimistic with z-index. But now I need to change that :)

Thanks for input,
And yes, I am on it, trying to make it draggable (not resizable yet but in pipeline).
:)

Hi there,
You may have tried this addon on addons.mozilla.org itself.
Please try this addon on other websites. And feel free to raise issues at http://github.com/tsl143/jsDemos/

I am not sure if I understood the request. All this addon do is, when you click toolbar button this create an overlay on screen and lets you to drag and select and area which gets the size of selected area in pixels.

Hi there,
This addon uses content-script API from webextensions API suite, which requires the aforesaid permissions. And this doesnt send or store any of your data, here is the code for this addon
https://github.com/tsl143/jsDemos/tree/master/measureIt_webext

I actually second your thought and even I find that permission intimidating, I have mailed Firefox team for same, hopefully we get a better solution.
Thanks again for input :)

UPDATE-
updated addon with different approach and without requiring website-data permissions :)