Firefox responsive issues?

Hi

We have a website on opencart 2.0.1.1 and are experiencing responsive issues.
In chrome all works fine when resizing but in firefox the moment you go smaller than 454px the majority of the website stretches back to full desktop width.

I am not seeing any errors in the console or any reason why this is occuring.
There is a log message which also starts appearing at this point though:

"invalid top tween value: NaN" jquery.themepunch.tools.min.js:98:2002
"invalid left tween value: NaN" jquery.themepunch.tools.min.js:98:2002

Any help would be appreciated.