Browser Compatibility and Chinese Letters

Hi, I would like to thank you for all the support you have given me so far, unfortunately I have realised some new issues with browser compatibility, specially IE and Firefox.

I have tested the website on chrome and safari on both Mac and PC and everything works perfect but when using IE 10 and 11, and firefox on PCs even with the latest versions of them all icons either disappear or show in some sort of Chinese letters or symbols.

The problem is also effecting other things too, for example the simple arrows displayed on the sides of easy slider or on the scroll to top function disappear and so on.

I have gone through many suggestion in your support section, from pasting codes to .htaccess, to installing suggested plugins and pasting codes to quick css but nothing is working.

I have also deleted all WordPress plugins and did a clean installation of your theme and imported the dummy data but nothing has been solved.

Here is the link to my domain: http://www.thamescad.co.uk/

Could you please help me. Thank you.