Some folks using Firefox 26 on OSX seem to be having difficulties posting classified ads.
Please use Safari or chrome while we try to determine the source of the browser incompatibility.
I have tested with Firefox 26 and personally have no difficulty OTOH I am also using OSX 10.9.2 developer seed, however all of the users reporting problems have been using this browser in conjunction with OSX 10.8.5 and 10.9.1