Writing Causes Page to Jump I have trouble writing on my Mac. 

It happens on pages on Safari like writing an e-mail or in Facebook and even in this question box. The problem is that the page starts jumping up and down as I'm writing and if I use the backspace key the page I'm on jumps back to the last page I was on, removing all my text.

How can I fix this?
most likely, one of two things is happening:

when you are typing you are accidentally touching the trackpad and moving or scrolling or clicking outside the text box you are typing in.

or when you are typing the case is flexing causing accidental clicks (heavy keyboard typists beware)

The clue here is the backspace functionality of the browser, as when inside a text entry field, the backspace works as a backspace delete, but when outside of a text entry, pressing backspace works the same as pressing the back button in the browser (i.e. go back to the previous page)