Rated 5 out of 5 stars
The review stars are for Version 0.5.0.4, not the version that it just (May 26 2018) updated to, 0.5.1. If I gave that a review, it would be one star because of all the functionality stripped out, presumably due to Firefox Quantum and its breaking of the addon environment.
That seemed unfair when I easily and successfully reverted to the prior version (just look at the app page and click "see all versions").
Things Tabs Mix Plus does for me:
Add an X to each tab so I can close it without focusing it or right clicking it.
Choose where new tabs and opened tabs go relative to the current tab
Adjust tab size so that I can see more
Greyscale tabs that haven't been refreshed so I know which will do some loading before I can view the web page.
Prevent popups and other links from generating new windows, opening them in tabs if at all.
A dozen other things that are simply part of my comfortable user experience.
Review is in Waterfox, which I switched to after Firefox 57 was released and broke addons in the ongoing quest to make every browser into a Chrome clone.
The update from yesterday was a mistake.
The latest beta is here: https://bitbucket.org/onemen/tabmixplus/downloads/tab_mix_plus-0.5.0.5pre.180526a1.xpi
I am currently working on Tab mix WebExtension, but it will take some time to rewrite all the code.