Doesn't work properly in v14b and v15a Rated 2 out of 5 stars
I manually placed the "Report" icon on the toolbar. Pressing it while selecting a message it says "No message are marked as Junk in the current folder".
Marking a message as Junk moves it into the Junk folder. If I use the "Report" button while in the "Junk" folder, it doesn't do anything. If I move a junk-marked message back to inbox so that I can use the report button (very convoluted) then it pauses for half a second and then nothing. I don't see any confirmation, I'm not sure it did report anything. I did so with 20 junk messages and it spent just as much time in that "pause" state as it did when there was only 1 junk marked message. Looks suspicious.
This extension should work on the messages that are highlighted (too), rather than only on those marked as junk; it should mark as junk at the same time to save clicks or awkward maneuvers (having to get all massages from junk into inbox and use the button again).