I've used the extensions Open Tab Next to Current and Always Right to open new tabs next the currently active tab. They work fine until New Tab Override is installed. After that, new tabs are opened 2 steps from the current active tab instead of right after. Hope this problem/conflict gets fixed.

Windows 10
Firefox 57.0.2
Tab Center Redux (Vertical Tabs)

Also wish there was a place to report bugs for New Tab Override instead of using ratings.