Try to do so:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful or accepting the risk.

(2) In the search box above the list, type or paste curr and pause while the list is filtered

(3) Then set:

browser.tabs.insertAfterCurrent = false (default)
browser.tabs.insertRelatedAfterCurrent = true (default)