1712247 - Hang when closing overflow menu by clicking near edge of arrow button with prefers-reduced-motion

Status: NEW

(Firefox :: Toolbars and Customization, defect, P3)

Description

[Adam Gashlin (he/him) [:agashlin] (ex-moco)]

Attachment: menu close hang

STR:

1. In Windows 10 Settings, under Ease of Access -> Display, turn off "Show animations in Windows" (this enabled prefer-reduced-motion)
2. From a new profile, customize the toolbar to put the Pocket icon in the overflow menu.
3. Click the >> button to open the overflow menu
4. Move the mouse cursor to the right edge of the button, past the highlight but before the next button (the hamburger menu) becomes highlighted
5. Click

The window stops responding. See attachment.

This does not reproduce if I turn the OS-level animation preference back on.

Crash via crashfirefox-intentionally: https://crash-stats.mozilla.org/report/index/f87fa528-4180-4d40-8525-465930210521

When I attach a debugger it seems to be running, common stacks are:

• mozilla::dom::EventTarget::AddEventListener for a popupshowing event
• mozilla::dom::Document::FlushPendingNotifications
  • nsIContent::GetPrimaryFrame
  • nsXULElement::HasMenu
  • mozilla::dom::XULElement_Binding::hasMenu
• also for mozilla::PresShell::FlushPendingNotifications
  • nsXULPopupManager::GetPopupFrameForContent
  • nsXULPopupManager::ShowPopup
  • mozilla::dom::XULPopupElement::OpenPopup

So it seems like it is stuck trying to pop up the menu over and over again.

The narrowest regression range I could get was between 2020-05-13 and 2020-05-14 (pushlog). Bug 1636057 seems the most likely immediate cause (seeing that in the pushlog is why I thought to reenable animations).

Bug 1708368 might be related as it's a hang when opening/closing the overflow menu. Bug 1633291 sounds similar for the hamburger menu, but without the hang, though I'm not able to reproduce that.