Rename this to _context_menu_locator for consistency. You used it here written without underscore:
https://github.com/mozilla-b2g/gaia/pull/13294/files#diff-6af581de0e257812a5a025d85b19a56bR62
and here with underscore:
https://github.com/mozilla-b2g/gaia/pull/13294/files#diff-ebf2198577aed5eff4b55e6c0c000c20R11