评分4星,满分5星

This compaction to a single line works fine. That displays subject and sender.

A problem arises with an email that has many addressees.
By default on the single line. To view the list one first clicks the + allowing just two names plus a More button to be displayed. C;icking More extends the list to fill the same line. But.... the clues that the list might be longer are a nearly invisible comma at the end of the row and a scroll bar. One must scroll down to see the rest of the list.
Now if one goes to another tab (say to check a detail in another email) and then returns to this tab ... one is back to just the first two names and the More button! To see the rest of the list, one must click more and scroll down again. This is a nuisance.
Suggestions:
1. Always fill out the line with as many names as will fit, with a trailing More button if there are more.
2. When the user has pressed More, expand the vertical space to display the full list (up to some large enough limit) and
3. leave the list displayed if the user temporarily goes to another tab and returns.

While thanking you for the extension, one must ask why TB 3 introduced all this confusion. We had none of this hassle with TB2.

这个评论是针对附加组件的一个早期版本的(1.1.4)。 

The behavior you describe is the default of Thunderbird. At the moment it is not changed by this add-on. I think you should file a bug at bugzilla.mozilla.org about the problem. I guess you really found a bug (switching between tabs) in Thunderbird.