I have no precise STR for this, but here are some paths to reproduce it : - Only happens when window is restored (not maximized) - Entering customize mode then enabling the DevEdition theme sometimes trigger this - Resizing the window manually by dragging an edge fixes the issue Usually happens in conjunction with bug 1187125. Intermittent issue.

with the menu button hovered instead of the close button

See https://bugzilla.mozilla.org/show_bug.cgi?id=1173725#c124 for more details

Tim, is it possible that this happens when you change your display scaling options in Windows (or use multiple displays)? We've had some issues there, all of which usually disappear once you log out and back in (as MS recommends)

(In reply to Philipp Sackl [:phlsa] (Firefox UX) please use needinfo from comment #6) > Tim, is it possible that this happens when you change your display scaling > options in Windows (or use multiple displays)? > We've had some issues there, all of which usually disappear once you log out > and back in (as MS recommends) The whole Windows session happens with 100% DPI, with a single display only. The issue disappears on Firefox restart.

The issue happened on Windows 7 and 8 when I was messing around with a custom window frame.

P4 with the same reasoning as bug 1187125.

(In reply to Tim Nguyen [:ntim] (mostly away until 26 August) from comment #8) > The issue happened on Windows 7 and 8 when I was messing around with a > custom window frame. This shouldn't block bug 1173725 then.

(In reply to Dão Gottwald [:dao] from comment #10) > (In reply to Tim Nguyen [:ntim] (mostly away until 26 August) from comment > #8) > > The issue happened on Windows 7 and 8 when I was messing around with a > > custom window frame. > > This shouldn't block bug 1173725 then. It should, bug 1173725 introduced custom caption buttons/window frame by default.

(In reply to Tim Nguyen [:ntim] (mostly away until 26 August) from comment #11) > (In reply to Dão Gottwald [:dao] from comment #10) > > (In reply to Tim Nguyen [:ntim] (mostly away until 26 August) from comment > > #8) > > > The issue happened on Windows 7 and 8 when I was messing around with a > > > custom window frame. > > > > This shouldn't block bug 1173725 then. > > It should, bug 1173725 introduced custom caption buttons/window frame by > default. I see. Do you know which part of that bug's patches exactly caused this bug then?

(In reply to Dão Gottwald [:dao] from comment #12) > (In reply to Tim Nguyen [:ntim] (mostly away until 26 August) from comment > #11) > > (In reply to Dão Gottwald [:dao] from comment #10) > > > (In reply to Tim Nguyen [:ntim] (mostly away until 26 August) from comment > > > #8) > > > > The issue happened on Windows 7 and 8 when I was messing around with a > > > > custom window frame. > > > > > > This shouldn't block bug 1173725 then. > > > > It should, bug 1173725 introduced custom caption buttons/window frame by > > default. > > I see. Do you know which part of that bug's patches exactly caused this bug > then? My guess is "-moz-appearance: window" on #main-window, which caused this.

Sounds like a widget or layout bug.