Update 19 April: script should work again.

You can use com-to-com to view the conversations between you and another user on your own profile, but what if you want to view the conversation between users on another profile? Just install this script that will add a com-to-com link for every comment on every profile!

You don't need to be logged in for this script to work.

This is a working version of MyAnimeList.net: Com-to-Com Links all credits go to N_Ox