Crap Rated 1 out of 5 stars

Doesn't work.

Hi, did you change any preferences? If yes which preference to what kind of value? What Firefox version and operating system do you use? What are you doing, what should the extension do and what does it actually do? (The default configuration and Firefox 51.0.1 on Windows 8.1 show expected behavior here: Middle-click on New Tab button next to current tab, else last tab to the right.)

Sober but interesting add-on, specially when tabs are a lot Rated 4 out of 5 stars

Really basic functionality that should be built-in for sure!

Some suggestions please :
-Add a double click option for opening new tab at the left of all the tabs...
-Add a line in default context menu when it appears after clicking on standard newtab "+", or anything else that can remember the add-on is here!

Simple useful add-on for users with many open tabs Rated 4 out of 5 stars

Very handy if you tend to keep a lot of tabs open and occasionally want a new tab next to the current one.
Works fine for my use case (thanks Archaeopteryx), but doesn't seem to work properly if you have changed browser.tabs.insertRelatedAfterCurrent to false (see: https://forums.mozilla.org/addons/viewtopic.php?f=28&t=11616)

Options also allow setting (unmodified) left-click, should you want to change the default behavior (thus it's also a partial replacement for Tab Control add-on, which is no longer maintained).