The easiest steps I know how to reproduce it is:
- open firefox (35 on my machine)
- type something in the search bar
- press escape to close the suggestion popup
- press backspace -> the suggestion popup should open with some suggestions in it
- keep pressing backspace while the suggestion popup is enlarged, because there are more suggestions.
When this happens the bottom of the suggestion popup is rendered black.
Running E19.1, EFL 1.12.2, both software and opengl compositors, nvidia drivers (9800gt card), xorg server 1.16.3-r1, gentoo linux 64bit.