This tabs issue has been fixed in Firefox 134. Search for 'browser.tabs.insertAfterCurrentExceptPinned' in about:config and change it to 'true'. Restart Firefox.

This is salvation! Thank you!

Brilliant🪄

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.

Works as expected.

I would have rated this 5 stars easily up until last week when it suddenly stopped working when I updated from v57.0 to v57.0.2 64x. No other addon installed OR updated. Will give proper rating if fixed.

I didn't realize the default behaviour was so wrong until I came across your add-on. Thank you!

Works as expected!

Such a pity, because I really need this, but it is not working on FF ESR 52.3.0 (32-bit)

EDIT: Old version doesn't work either (replying to developer's answer):
Thank you for your reply, it's not that often that a dev keeps caring about people's feedback. I tried installing version 2.0.7 (and yes, I uninstalled the add-on first, then restarted FF, installed 2.0.7, and restarted FF) and no changes, the pinned tabs still appear on the left. Is there anything I should be doing apart for pinning the tab?