firefox 11 cannot change arguments for a panelizer variant

Create a panels page with a path like 'string/%nid' panelizer variant, and you will get a big ajax error message (that actually doesn't contain an error, and just displays page text) when you try to change the argument.

This is firefox only so far as I can see - it works fine in webkit browsers like Chrome.

Bonus oddity: this functionality works in firefox if the path is 'node/%wildcard' but not if it's 'notanode/%wildcard'.