Used to access webmail on my website via Firefox but since upgrade to V4 I now get the reply "Remote XUL This page uses an unsupported technology that is no longer available by default in Firefox" Can I get a fix for this?.

I run a website www.brooktrust.org, hosted by Moonfruit. The web mail account provided with the site is used regularly. Under previous versions of Firefox I was able to log on, but now I get a message teling me that the page uses an unsupported technology "Remote XUL" and I should inform website owner. I am the website owner and I want to know if I can add the technology to Firefox or need to add something at the website end. I have tried to raise the issue with Moonfruit.