Screen distortions when using Firefox on Android

Hi, a recurrent problem - when using Firefox on my Android, websites are often displayed distorted. If I try to zoom in to increase the font or image size when reading, the screen tears and distorts, with different sections of text and images disappearing altogether (black sections of screen appear) or overlapping, often in different font sizes. The website displayed on the screen also "jumps around". The same happens if I try to select text for copying - it is either impossible to select at all, or the selection is distorted. I haven't had this problem before and noticed it only recently. Almost impossible to use the browser now! Could that be a result of an automatic software update? Please help! Thanks.