new post/reply screen format screwed up

[Zelda Pinwheel]

For a while now, anytime I try to reply to a post or start a new topic, the page is formatted weirdly, all squished up on the left-hand side and a tiny box for the message itself:




I'm using Firefox 12 but it seems to be the same in Chrome and IE.

Is it just me? It does make it quite hard to format messages when i've only got a width of 20 characters to play with.