click on Mailbox expand into left pane? plz

[Walther von Vog]

This would be similar to classic dual-pane file managers. With those, clicking on a folder expands the contents in the existing pane, rather than opening into the opposite pane. What I want is a toggle for when I'm opening a mailbox in Classic view to display the contents in the leftmost Mailboxes pane instead of the main mail panel. So many times when I'm dragging a message from Main to a mailbox I've dropped it into the adjacent box or some other, then have to go find it. With the mailbox content expanded on the left it would be nearly impossible to drag wrong. And yes, I know about context/Moveto but often the list there de-populates, no idea why. I prefer dragging anyway.

Is there some built-in control for this, or maybe an add-on?

[tanstaafl]

Locked. Duplicate of http://forums.mozillazine.org/viewtopic ... &t=3032947 .