In ff v0.1.3, the slowness is reduced to some extent.

  > ff '.*.js' ~/projects > /dev/null  
  5.79s user 
  14.77s system 
  97% cpu 
  21.024 total

  > find -E ~/projects -type f -regex '.*.js' > /dev/null  
  3.98s user 
  10.76s system 
  67% cpu 
  21.933 total