This new tool lets you see which of your matches match each other.
You can access it by selecting "Matrix" in the pull-down Family Finder menu. You can then select who you want in the Matrix, and see if they appear in each others Family Finder match lists.
This is not quite as useful as the ability to compare two matches to each other that can be done at 23andMe or Gedmatch, but it is still a great tool.
The reason its not quite as useful as the ability to compare two matches to each other is that if DNA Cousin A matches you in a segment, and so does DNA Cousin B, even if they match each other in the new Matrix tool, the match could be in another segment, and therefore not necessarily from the same common ancestor.