Same behaviour confirmed here. Only happens in FF, and does not happen with non-async JS tags. Current install (3.2.1). It doesn't seem to stack in the history, oddly. ie. start on homepage, see 1 or 2 (can't tell what causes the random choice of how many) extra history entries. Navigate to a new page, new page has 1 or 2 extra entries but the previous page now just shows the one entry. My guess is this is a bug in FF, but maybe something that can be worked around easily? Can view the issue on bigclassaction com and am happy to make tweaks on the site to help debug.