I've been having trouble logging in to Spotify since moving to Mint 18.2.  The current stable release of spotify-client doesn't seem to successfully work with firefox.  I resolved the issue by updating my sources file (/etc/apt/sources.list.d/spotify.list) to

deb http://repository.spotify.com testing non-free

then running apt-get update and apt-get upgrade

Pro:  the login dialogue for Facebook works again

Con:  it is a testing release.  I haven't used it much yet but so far so good.

Yay tunes..