Rated 4 out of 5 stars

Quite nice.

One problem: For conversations where I have replied to a mail but not received an answer back, it doesn't seem to be possible to get the GMail conversation view. Is this because of Thunderbird limitations (doesn't recognize as a conversation)? I would very much like this ability.

This review is for a previous version of the add-on (0.3alpha1). 

The add-on doesn't automatically recognize this as a conversation. This would add a lot of extra code which I don't want to start right now, as I need to improve other parts of the add-on. However, it is planned and will be done in a future version.

For those messages, right now, you can just customize the toolbar, add the "view full conversation" button and use this to switch to the conversation view.