Rated 4 out of 5 stars
I very much appreciate this add-on, and even with a small bug found, I'll continue to use it for as long as I can.
The bug: version 22.214.171.124 of this plugin with current Thunderbird (31+), prevents large image resizing to fit the preview window-pane. So if someone sends you an image larger than can be viewed in Thunderbird, you'll have to save the file and resize it using your image viewer/editor.
Quite old review, but for the reference: this should be fixed in 1.1+.