Форум сообщества Firefox для Android

I have a vivo pad 3, and when I'm using it in landscape mode, the firefox app would only occupy part of the screen, leaving the two sides empty. It used to work fine and I don't know what made it to behave like this since I didn't touch the settings, and no other app is like this.

I don't know from which version of FF it started exactly, but recently loading of websites starts after huge pause or fails at all, the same is with elements of web pages if those are located on different domain. This is only FF problem, other browsers load pages instantly. I have tried to delete cache, data and FF completely and reinstall anew, it doesn't help. I can only guess what causes it, probably some DNS connection issues.