Since we aren't caching the folder sort strings at all, this results in O(n^3) runtime, although the horror would only be realized if all folders were nested in a single super-deep tree with no branches.

In any event, account._folderInfo[folder.parentId] should work.  It's fine to be poking at the underscore stuff from here.  We just wouldn't want general consumers poking at the map; they should use the helper functions.