Tab ownership stops working properly when more than one link is opened from a tab
In the scenario where I have multiple tabs open
... [Tab A] [Tab B] ...
and I open several links from [Tab A] such that my new tab layout is
... [Tab A] [Tab X] [Tab Y] [Tab Z] [Tab B] ...
In other browsers tested, closing the new tabs from either X -> Z or Z -> X will both result in [Tab A], the owner/parent tab, being focused.
In Firefox, closing the tabs in either order will close the tabs in order to the right, resulting in [Tab B] being focused instead. Only in the case where a single tab was opened from [Tab A] will the selectOwnerOnClose property work correctly and focus [Tab A].
To give a realistic example, sometimes when browsing Reddit with some other tab open to the right, I like to open new tabs for several threads at once, and because this breaks the selectOwnerOnClose functionality it is mildly inconvenient/inconsistent.
Before the Quantum update, I had installed Tab Mix Plus to solve this inconsistency, but as that extension is now legacy, I am reminded of the issue.