Karl Tomlinson (:karlt) Reporter
	Description • 8 years ago

1. Customize menu bar UI to include some buttons.
2. Open some tabs and make the foreground tab one that is away from button
   to test.
3. Hover over background tab below button to test.
4. Move pointer quickly to hover over the button.
5. If bug does not reproduce then repeat from 3.
6. Move pointer away to left or right or above, to leave bug visible.

Expected: continuous line between menubar and tabbar.
Actual: white chunks remain.

GTK Theme: Adwaita 3.18.19

Adding overflow from GetExtraSizeForWidget() for NS_THEME_TOOLBARBUTTON shows the white shadow consistently.

Looks like this comes from:
  box-shadow: inset 0 1px white, 0 1px white;

I didn't reproduce on win7, nor with other GTK themes.

Regression range
https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=336a70a8dfe4a980627b43da56c8b93658d3fba9&tochange=f5de44ecf07f3cbd369015663b72d452fda6d177
identifies the trigger to be bug 1236043, but I doubt that is the problem.

	Karl Tomlinson (:karlt) Reporter
	Comment 1 • 8 years ago

I haven't seen this happen in common configurations.