The localization for lt Firefox is currently not on the trunk, it was initially checked in on the MOZILLA_1_8_BRANCH. We need to merge that back to the trunk at some point, though I'm not sure which. We could do now, or we could wait for fx2 to complete, that depends a bit on how you want to work on it.
Firefox translation from MOZILLA_1_8_0_BRANCH is checked into the truk. I'll update it to Fx 2 when it is finished on MOZILLA_1_8_BRANCH.