I was trying to post on JJ's blog, but it also happens on my blog and some threads here. Also with PMs.
I was really surprised that thread got through.
Okay, it must be specific to my computer, because the work computer has no issue with it. I'll reset all my stuff when I get home.
As far as I could tell it only worked when creating totally new threads or blogs. Creating subsequent posts or attempting to edit anything sent me to the blank page.