Rated 5 out of 5 stars

Beta3 prevents attachments from being opened. Stick with the v1.2.4.
Edit: Tested 1.4.0 Beta1. I can confirm this issue is fixed (either by author or tbird update.)
Upgraded rating to 5 stars. Mozilla should have made this a feature.

This review is for a previous version of the add-on (1.2.4). 

Probably a bug core bug of Thunderbird which was fixed in 3.1.5

Subject says it all: This bug seems to have been disappeared with the release of Thunderbird 3.1.5. Could you please check.

Rated 3 out of 5 stars

Better, but doesn't fix the biggest problem: The use of a small font with really big line spacing.
3 lines isn't out of the question if you could reduce all the empty space.
2 lines could be more compact if you relocated the email's date... because it really is 3 lines high with a blank line #2.
My only other complaint is that the 'flat buttons' cause the width of the header to get fatter when you mouse over them... it's a bit sloppy looking.

This review is for a previous version of the add-on (1.2.4).