Rated 4 out of 5 stars

"You found the very first listing, when the addon was just released..." Wrong. This is the fifth time this extension has been in the "recently updated" report. Limited rating to 3 stars because you deleted the review after replying with sarcasm. You didn't need to put it here for testing. You could have sent the xpi to people.
My initial post was out of frustration with insufficient descriptions. Maybe somebody from Mozilla deleted it. They should stick to making software. I apologize for snapping at you.

I prefer ThunderStats!'s information and Mail Summaries' color scheme.

Ideas to increase legibility:

Use account overview page, not a separate tab.

Reduce overall vertical size; overviews should not have scrollbars on laptops - investiagate dynamic spacing. Reduce visual clutter; use color or position whereever possible, not both. Choose scheme with more complimentary colors. Reduce color count. Always use dark font on light background. Add total, yearly, and monthly time span tabs. Remove dark blue and reduce height of tabs. Center quadrant titles.

Top quadrants: Increase left/right borders inside quadrants; contents too close to borders. Current axis labels are too dominant; reduce them. Swap contents of upper quadrants. Label today's mail bar chart with clock time or day/evening/night and reduce color count to sent/received. Words "Sent" and "Received" should be in appropriate color, not swatches with black labels. I do not see any usefulness for vertical inbox date bar chart; enlighten me.

Bottom quadrants: Remove colors from charts. Add thin horizontal line between lines 5 and 6 of columns 2 and 3.

This review is for a previous version of the add-on (0.5). 

I didn't even know it was possibile to delete a review.
Btw, you didin't review the addon with your first review as you didn't with this one.
As for the "fifth time", you're right, I was releasing some beta versions given the feedback I receive and I forgot to update the listing, that was the very first I published with version 0.1. Is that a so severe problem?
May I ask you to acutally review the addon? Have you tried it?

==== UPDATE ====
Thank you for testing this preliminary version of the addon.
Thank you also for your many suggestions! For quadrants content, that I'm calling widgets, I'm going to let the user choose which widget to show and where: https://github.com/micz/ThunderStats/issues/12
and I'm going to add more widgets: https://github.com/micz/ThunderStats/issues/61
For the colors scheme, I've added now this issue: https://github.com/micz/ThunderStats/issues/82

The vertical date bar chart is useful to know how many old emails are still in the inbox. It could be useful if you manage your inbox with the "Inbox Zero" methodology.

I'm going to add a custom time span tab in a future version: https://github.com/micz/ThunderStats/issues/67
It could be slow, wo I was wondering also about some kind of data consolidation: https://github.com/micz/ThunderStats/issues/9
You could find all the new features here: https://github.com/micz/ThunderStats/labels/new%20feature

I'll try your others positioning/ui-improvements suggestions. Thanks you.