The site has always been very very slow in Firefox. I just got a new computer running 32-bit Windows with the maximum 4GB memory, and Firefox will lock up if I open more than 2 or 3 tabs in your site. The status bar shows that you're trying to contact a never-ending number of other sites and "establishing TLS handshakes" and so on. It's now unusable.
Meanwhile in Chrome, everything works very very well. So it makes me wonder if you test the site performance in different browsers or OS's. There's no way you could look at the site in FF and deem it acceptable.
Customer support service by UserEcho