794756 - downloads panel occasionally appears at the wrong position (extreme left of window)

Status: RESOLVED DUPLICATE of bug 751947

(Toolkit :: Downloads API, defect)

Description

[Jonathan Kew [:jfkthame]]

Attachment: downloads panel failed to attach to its button

When I click the Downloads button in the toolbar, to display the Downloads doorhanger panel, the panel is *sometimes* (but only occasionally) misplaced, appearing at the left of the browser window instead of "attached" to the button.

This only ever occurs the first time the button is used during a browser session; repeating the operation will consistently display the panel in the proper location.

Attached screenshot shows the panel being displayed in the wrong position.

I suspect this might be related to bug 794752, which notes that on this first click, the Downloads button adjusts its size slightly. If the button is in the midst of this (unwanted) size-change at the moment the panel tries to place itself, perhaps that's when it fails to get the proper position.

I see this more often in my local debug builds, but have also reproduced it with the official Nightly. This is consistent with the idea that the problem happens only if the positioning of the panel races with the adjustment to the button it's meant to be attached to; in a (slower) debug build, there's a larger window of opportunity for the problem to appear.