Clicking on the button to create a new private message, appear a box with some fields. Clicking on the the body field, the focus switches correctly and the caret start blinking but every pressed key is ignored. The problem affects at least the last 3-4 nightly version. There is no problem with Safari 3.0.4. The test has been done on a MacBook Pro with the apps launched in 64 bit mode on the default 32 bit kernel.
*** This bug has been marked as a duplicate of bug 29815 ***