In firefox fenix, I see team is working on wallpapers feature but the wallpapers colors does not match with rest of the screen colors. So except default wallpaper all others feels like aliens on the homescreen
So instead of wasting time in implementing wallpaper and adjusting other items color based on the wallpapers, why not use static theme like firefox colorways? This can color the toolbar and the menu too . I know firefox android can never support full pleged themes like desktop but atleast you can give predefined colors such as firefox colorways...
Opera gx android browser already has this feature