when my screen turns ff wont load properly - i get 5 pages nest to each other all with horizontal lines through them

I can load firefox ok on my phone and it works fine - until I turn my phone horizontal (to get the width of the screen) and then all i see is the web page in the bottom half of my screen - but 5 times all next to each other and with loads of lines through the bottom half of the screen. It is not my phone as when I use the android browser its fine. I use firefox as I can sync it with my desktop, Please can you find a solution for me as at the moment I cant use firefox now (dont have that wide a screen to view normally).

I have the latest version of firefox on my phone (as I did an update hoping this would solve the problem - but no joy).