Tabs are open in reverse order when "browser.tabs.insertAfterCurrent" is true.

To answer your questions
I'm running Firefox 55.0.3

As for URLs there are many . Here are a few examples.

A list of zippyshare URL's on numerous occasions
A mixed list of music and storage sites (i.e. youtube, mediafire, zippyshare, discogs) etc

I even just tried the list of sites I have in my menu bar (ebay, amazon,imdb) etc . It failed too.

This is a generic problem and not url specific and it occurred when your add-on changed from 'legacy'.