White areas when opening a new tab and search.

Hi guys!

When you open a new tab, the area of ​​the tab itself becomes white, the same thing happens when you open the search (ctrl+f). This becomes noticeable when using a dark theme. This can be fixed by the settings:

ui.systemUsesDarkTheme=1 and browser.in-content.dark-mode true

I think this is worth adding here, as well as the documentation.