Hello Phil.

I can replicate that problem in my installation but if I try to disable all extensions (you can do that by running Firefox in safe-mode) the site works ok, so, at least from my side, it's a problem with one (or more) of my extensions. I recommend you run firefox in safe-mode to disable all extensions, see if it works. If it does, try to enable one extension at a time until you find the one that's causing trouble, then disable it and contact its author for support.