Thanks for review.
Are you sure you're using the latest version (v3.1.0) ? Because I know for sure that I fixed this problem a while ago and I can't really seem to replicate it on my end no matter how much I try. The order you see them in the list (top-down) should be the exact order of tabs. I know that Firefox somehow saves a list of bookmarks in reverse order but if they are saved correctly I make sure that the order in which I open the tabs is that one. I will look into it more but I verified and unless there's a strange bug happening the latest version should have fixed that.