In today's nightly build, we are not seeing any devicemotion events. On Android, I do see the system sending the data to our process. On the Mac, it is also busted (but might be related to my recent Lion update; not sure about that yet).
from Bug 673472. I should have caught this in the review of the patch, but didn't. Small logic error in AddWindowListener. http://hg.mozilla.org/mozilla-central/rev/bc1a1ecbb82e