Layout breaks in Mozilla Firefox

Question

Mozilla

In Opera, IE, Chrome browsers, the site is displayed correctly, exactly as I set it in css styles, and in Mozilla Firefox, the content block becomes wider and the sidebar goes down. A block with 700px wide content and a 20px right margin, a 220px wide sidebar, all wrapped in 940px.
Here is the site clickprime8.info/.

Answer 1

Try to put a vendor prefkis for the box model for fox:
caniuse.com/#search=box-sizing