if u bought ur car new, it doesn't have an LSD. all focuses came w/ open diffs. (i can't say for the new 2012's, but if you have a pre-'12, then unless someone put it in for you as in the previous owner, it didn't come w/ one.
terminator v8 in an SVT focus (soon to be boosted @ 20 PSI with a 2.9 L Kenne Belle on Corn!!!
(750 rwp and low 10 second focus, here I come!)