Starting with Firefox 30, you'll be able use position on table components. You can try for yourself with the current nightly build (works as standalone): http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-trunk/
Test case (http://jsfiddle.net/acbabis/hpWZk/):
You can continue to follow the developers' discussion of the changes here (the topic is 13 years old): https://bugzilla.mozilla.org/show_bug.cgi?id=63895
Judging by recent release history, this could be available as soon as May 2014. I can barely contain my excitement!
EDIT (6/10/14): Firefox 30 was released today. Soon, table positioning won't be an issue in major desktop browsers