Thanks for the tips.
I'm no JavaScript expert, but it looks like the offending line is #335
function change_category(cat, char, dest) {
I think mozilla is getting confused thinking that 'char' is a type, not a variable name. If I change it to 'chr' on a downloaded version it seems to make it past this part (but it breaks elsewhere, probably because I don't have the rest of the infrastructure in place).
Hope that helps.