Facebook did something horrible to their user interface recently, perhaps trying to make it more Twitterish by submitting a comment as soon as a user presses the Return key.
Daniel Wood, on his blog, wrote and posted a small Chrome extension that looks sane and which was supposed to solve the issue; I downloaded it and fixed a problem with the headers which were set up to tweak “facebook.com” pages rather than “www.facebook.com” pages.
I have posted my version here, but I make no claim on it, and I accept no responsibility for it.
If you use
www.facebook.com, though, it seems to fix the pain.