This example should be straightforward, as you can see the title bar on the bottom has a dark blue color from the source app (Tusky) while the navigation bar is white. On Tusky the navigation bar is the same dark blue as the title bar.
I'm not sure if Android allows getting the color of the source app's navigation bar, but anything could be better than a pure white one especially when the title bar is put on the bottom. I suggest Firefox to use either 1. Same color as the title bar 2. A slightly darker version of title bar color.