For information :

I have got the site working on another web host (which may be faster and therefore able to cope with the problem).

The problem seems to be a problem with Firefox no longer catering for javascript and the server times out while trying to trying to do something with it (that's about the level of my understanding).

A Google analysis says I should fix:
Eliminate render-blocking JavaScript and CSS in above-the-fold content
Your page has 2 blocking script resources and 6 blocking CSS resources. This causes a delay in rendering your page.
None of the above-the-fold content on your page could be rendered without waiting for the following resources to load. Try to defer or asynchronously load blocking resources, or inline the critical portions of those resources directly in the HTML.
Remove render-blocking JavaScript:
http://pyramidfolk.co.uk/index_htm_files/roe.js
http://pyramidfolk.co.uk/index_htm_f...MobileFonts.js

As these files are generated by Xara what am I to do? Apart from raise a ticket with Xara which I have already done.

I've wasted days and spent money on a problem which appears to have resulted from Xara DP producing some duff code. Am I being too harsh here?