Rated 5 out of 5 stars
@Drakulian - I had this problem too.
I found "ColorfulTabs" (v4.1 as I type) conflicted with "Closy" (v1.4.0). I will live without pretty colors for my tabs so I can close dup tabs (why this addon is fantastic). So "ColorfulTabs" got disabled and "Closy" works well.
PS To author of "Closy" maybe you can research the conflict with "ColorfulTabs" and hopefully resolve the problem? Thanks!