Waterfox 1.1.7 (Build #2025468809)
Opening the tab menu by pressing the tab button on the navigation bar, and then pressing pressing the new tab button, gives you a black screen instead of the home screen. Additionally, pressing on the black screen will interact with the home screen (shortcuts can be triggered like this).
This doesn't happen in Firefox Mobile.

Actually I just realized it's black because that's my theme, it fills the screen with the theme color (if it's of any help)