After the addition of the browser.tabs.insertAfterCurrent setting in about:config you do not need this extension anymore.

ok, fast, easy :)
BUT after closing tab it jumps alspo to the right.
Could it jump to the left it opening tab? :)

Excellent! One more to make up for the missing TMP.
Always opens new tabs to the right of the currently active tabs.
The only inconsistency in this behaviour is when pressing the + button to the right of the open tabs. In this case I would expect the new tab to open at the end of the list.

It worked quite good, solved my problem at the beginning. However, if multiple tabs are opened with "open link in new tab" but not activated, the newly opened tabs will be inserted to the right of the newly inserted inactivated tabs, but not the current tab. Possible to fix this? Thanks.

59.0.2 (32-bit)
After some time working correctly, just recently I find tabs opening at end of line again.

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It's absurd this isn't the default.

Using Nightly [now 58.0a1 (2017-10-07) (32-bit)] sometimes ctrl_T goes to end-of-tabs instead of the next slot,

Just now, I did ctrl_T from the frst tab, it went to th end of the line; I moved it back manually.
Next I tried it on a mid-tab: fine, it went to next slot.
Tried again on first tab, this time it worked properly.

I suspect it's a photon glitch, some module not loading in time without being checked. Is there a way to ensure it works always?

Additionally, when I ctr_T on the first tab in the visible row, it not only creates a tab, but shifts focus to it (which is an assumption too far), and moves the current tab leftwards out of view. So I then have to move left again to see where I was.

The search function also changes focus to the search page rather than opening it in background. So, if I need to search for several items on a page, I have to go back & forth each time.Could be another piece of slack thinking by mozilla.