For years I've been having this problem and after looking for solutions multiple times I found this thanks to a comment on a Bugzilla report from 9 years ago. Works as expected, when opening a new tab from a pinned one it will go the last position instead of the fist. The only downside is that for a split second the tab list will scroll all the way to the left then all the way to the right but I can live with that.

After updating to the latest version whenever i click the new tab button it jumps back to the previously selected tab. Removing this addon solves the issue.

EDIT: Thanks a lot for the reply, glad to see a dev keeping in touch with his users!

EDIT 2: Works perfecty now! Thanks again!