According to the documentation, the insertafter attribute should insert the new node after the first id found in the comma separated list. This was indeed the behavior I was experiencing in my add-on Mail Redirect in Thunderbird 60.* and before. In Thunderbird 65 however, the new element is inserted after the last id found in the list. There's of course a workaround, by specifying insertafter="a,b,a", but it would be best if the XUL Overlay Loader did this the same way it used to work. P.S. The same problem might apply to the insertbefore attribute, but I didn't use that in combination with a comma separated list in my add-on and I haven't tried it.

I've tested this against ESR60 and the comment in the code is just wrong.

Comment on attachment 9032388 [details] [diff] [review] 1512581-overlay-insertorder-1.diff Review of attachment 9032388 [details] [diff] [review]: ----------------------------------------------------------------- Yep, you are right. Not sure what I was thinking there.

Pushed by geoff@darktrojan.net: https://hg.mozilla.org/comm-central/rev/8a7f1cf1ba4e Match original behaviour of insertbefore/insertafter attributes; r=Fallen DONTBUILD

Beta (TB 65): https://hg.mozilla.org/releases/comm-beta/rev/994a012451923d399d70cb0b00cb63146e2ac312