Rated 3 out of 5 stars

Good idea and implementation overall that helps with keeping an overview of message threads / conversations. Though I noticed a couple of issues that may be a showstopper or at least a drawback for many users (myself included):
1. Does not work properly with dark themes. Backgrounds of messages (in read mode) are always set to white by default.
2. Font sizes in the message pane are fixed by default and cannot be altered -> REALLY bad thing for people with visual impairments who want to zoom in on messages to magnify font display.
3. Messages by default open in a fixed-sized window that gets aligned to the left of the screen and extends across the entire height of the screen. Why?
4. Attachments always get displayed at the end of a message which can mean a lot of additional scrolling effort.
Neither of these behaviors can be adapted anywhere in the settings, at least not that I would see it. I feel this is quite restricting in relation to the “core” benefit of having messages threaded into conversations.
Instead of “forcing” users into the above restrictions, the extension should focus on its core value added which is grouping messages by conversation – and not “fiddle around” with diverse default layout and display options – at least not without enabling users to turn these off again.

This review is for a previous version of the add-on (3.2.17).