A few suggestions from version 0.4.5:
- The subject should be left-aligned with the sender.
- The "other actions" button should be right-aligned with the right-most button (usually the Trash button).
- The default preferences should be:
- Display two lines
- Show only icons inside buttons
- Buttons shown:
- Reply
- Reply All
- Forward
- Trash
- Tags should also be shown in the compact view - possibly between the recipient and the buttons.
- There should be separate [Reply] and [Reply All] buttons that are both always visible. The automatic Reply-All is especially annoying.
- Upgrade the version number of your add-on to 1.0 because it's already light-years better than Thunderbird 2s or 3s headers!