Hi, James.Thanks for the tip. This issue seems to be related to Moodle's use of YUI.
After reviewing different settings of Java and FF 18 we cleared the cache and cookies. Drag and drop is now working for us.
For me personally, moving activities and resources up and down within a course page is still not possible in Chrome (both in Moodle 2.4 and 2.5). Is this correct?