Firefox Add-ons へようこそ。
New tabs should always open to the immediate right of the current tab. And now they will.
Usually when I open new tabs, it's not because a lightning bolt struck, and I must switch from my current activity to a new and different one. Most of the time the new tab is directly related to what I'm currently doing, so when Firefox opens tabs at the end of 50 tabs, they're almost guaranteed to be far from the tabs I was working with. I then find myself hunting around for the tabs I was just at, sometimes trying long and RSI-inducing drag-and-drop operations to regroup things.
Sure, if I wanted to strictly manage things, I could always have separate Panorama groups in this tab set, but often my workflow is more organic than that, and I end up in this place, and I should be able to continue working with the software in the way that my mind expects it to work.
So maybe this isn't for you, but I'm Always Right.
Known issues with WebExtension version (2.0.4 and up), due to limitations of WebExtension implementation in Firefox:
* Tab strip scrolls to position of new tab, instead of staying in same place
* With lots of tabs, the scrolling becomes visually annoying