Relative positioning of table rows and row groups is now supported. This site may need to be updated because it may depend on this feature having no effect.

Firefox displayed this warning in the Firebug console.  This warning indicates an absolutely positioned does not consider a table element relatively positioned so it may not appear as expected.  A better explanation is here:

https://www.sencha.com/forum/showthread.php?289315-Relative-positioning-of-table-rows-and-row-groups-is-now-supported.-This-site-may-nee

and solution to fix is here:

http://stackoverflow.com/questions/5148041/does-firefox-support-position-relative-on-table-elements