Very much would do what I was looking for - unfortunately I have to agree with the previous comment that it works very inconsistently.

There are some cases where it works as expected, but especially for tab activation after closing a tab it is really un-predictable where it jumps to ... especially if you have been changing tabs in between.

In some cases also opening the tab (I have set it to right) does not work but opens at the end ...

I hope that this will be updated and improved as I could not find any other add-on providing this functionality (still hoping for TabPlus one day :-) ).

PS: I do not know / understand what the author wants to indictate with those lines:
btw:
about:config -> browser.tabs.insertRelatedAfterCurrent -> true
about:config -> browser.tabs.selectOwnerOnClose -> true
Would that indicate that this setting is needed for the add-on to work correctly (it does not), or are those settings changed by the add-on? Some more information might be helpful to improve that add-on ....

PS: Unfortunately the author does not seem to respond to the issues and there has been no update for adressing them ...